[WRR] implement non-per-call metrics (#35977)

As per gRFC A78 (https://github.com/grpc/proposal/pull/419). Note that these new metrics are populated only if the `wrr_delegate_to_pick_first` experiment is enabled, which is the case by default. Closes #35977 COPYBARA_INTEGRATE_REVIEW=https://github.com/grpc/grpc/pull/35977 from markdroth:non_per_call_metrics_wrr 7acea32fc4 PiperOrigin-RevId: 610760874
2024-02-27 08:29:50 -08:00 · 2024-02-27 08:29:50 -08:00 · 40577dd585
parent 571da7be78
commit 40577dd585
38 changed files with 916 additions and 326 deletions
--- a/1
+++ b/1
@ -1817,6 +1817,7 @@ grpc_cc_library(
        "//src/core:message",
        "//src/core:metadata",
        "//src/core:metadata_batch",
+        "//src/core:metrics",
        "//src/core:no_destruct",
        "//src/core:per_cpu",
        "//src/core:pipe",
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@ -2210,6 +2210,7 @@ add_library(grpc
  src/core/lib/channel/channelz.cc
  src/core/lib/channel/channelz_registry.cc
  src/core/lib/channel/connected_channel.cc
+  src/core/lib/channel/metrics.cc
  src/core/lib/channel/promise_based_filter.cc
  src/core/lib/channel/server_call_tracer_filter.cc
  src/core/lib/channel/status_util.cc
@ -2977,6 +2978,7 @@ add_library(grpc_unsecure
  src/core/lib/channel/channelz.cc
  src/core/lib/channel/channelz_registry.cc
  src/core/lib/channel/connected_channel.cc
+  src/core/lib/channel/metrics.cc
  src/core/lib/channel/promise_based_filter.cc
  src/core/lib/channel/server_call_tracer_filter.cc
  src/core/lib/channel/status_util.cc
@ -5103,6 +5105,7 @@ add_library(grpc_authorization_provider
  src/core/lib/channel/channelz.cc
  src/core/lib/channel/channelz_registry.cc
  src/core/lib/channel/connected_channel.cc
+  src/core/lib/channel/metrics.cc
  src/core/lib/channel/promise_based_filter.cc
  src/core/lib/channel/server_call_tracer_filter.cc
  src/core/lib/channel/status_util.cc
@ -19563,8 +19566,8 @@ endif()
 if(gRPC_BUILD_TESTS)

 add_executable(metrics_test
-  src/core/lib/channel/metrics.cc
  test/core/channel/metrics_test.cc
+  test/core/util/fake_stats_plugin.cc
 )
 if(WIN32 AND MSVC)
  if(BUILD_SHARED_LIBS)
@ -31749,6 +31752,7 @@ if(gRPC_BUILD_TESTS)

 add_executable(weighted_round_robin_config_test
  test/core/client_channel/lb_policy/weighted_round_robin_config_test.cc
+  test/core/util/fake_stats_plugin.cc
 )
 if(WIN32 AND MSVC)
  if(BUILD_SHARED_LIBS)
@ -31797,6 +31801,7 @@ add_executable(weighted_round_robin_test
  test/core/client_channel/lb_policy/weighted_round_robin_test.cc
  test/core/event_engine/event_engine_test_utils.cc
  test/core/event_engine/fuzzing_event_engine/fuzzing_event_engine.cc
+  test/core/util/fake_stats_plugin.cc
 )
 if(WIN32 AND MSVC)
  if(BUILD_SHARED_LIBS)
@ -36106,6 +36111,7 @@ if(_gRPC_PLATFORM_LINUX OR _gRPC_PLATFORM_MAC OR _gRPC_PLATFORM_POSIX)
    ${_gRPC_PROTO_GENS_DIR}/src/proto/grpc/testing/xds/v3/wrr_locality.grpc.pb.cc
    ${_gRPC_PROTO_GENS_DIR}/src/proto/grpc/testing/xds/v3/wrr_locality.pb.h
    ${_gRPC_PROTO_GENS_DIR}/src/proto/grpc/testing/xds/v3/wrr_locality.grpc.pb.h
+    test/core/util/fake_stats_plugin.cc
    test/cpp/end2end/test_service_impl.cc
    test/cpp/end2end/xds/xds_end2end_test_lib.cc
    test/cpp/end2end/xds/xds_server.cc
--- a/2
+++ b/2
@ -1391,6 +1391,7 @@ LIBGRPC_SRC = \
    src/core/lib/channel/channelz.cc \
    src/core/lib/channel/channelz_registry.cc \
    src/core/lib/channel/connected_channel.cc \
+    src/core/lib/channel/metrics.cc \
    src/core/lib/channel/promise_based_filter.cc \
    src/core/lib/channel/server_call_tracer_filter.cc \
    src/core/lib/channel/status_util.cc \
@ -1992,6 +1993,7 @@ LIBGRPC_UNSECURE_SRC = \
    src/core/lib/channel/channelz.cc \
    src/core/lib/channel/channelz_registry.cc \
    src/core/lib/channel/connected_channel.cc \
+    src/core/lib/channel/metrics.cc \
    src/core/lib/channel/promise_based_filter.cc \
    src/core/lib/channel/server_call_tracer_filter.cc \
    src/core/lib/channel/status_util.cc \
--- a/Package.swift
+++ b/Package.swift
@ -1155,6 +1155,8 @@ let package = Package(
        "src/core/lib/channel/connected_channel.cc",
        "src/core/lib/channel/connected_channel.h",
        "src/core/lib/channel/context.h",
+        "src/core/lib/channel/metrics.cc",
+        "src/core/lib/channel/metrics.h",
        "src/core/lib/channel/promise_based_filter.cc",
        "src/core/lib/channel/promise_based_filter.h",
        "src/core/lib/channel/server_call_tracer_filter.cc",
@ -1890,6 +1892,7 @@ let package = Package(
        "src/core/load_balancing/weighted_round_robin/static_stride_scheduler.h",
        "src/core/load_balancing/weighted_round_robin/weighted_round_robin.cc",
        "src/core/load_balancing/weighted_target/weighted_target.cc",
+        "src/core/load_balancing/weighted_target/weighted_target.h",
        "src/core/load_balancing/xds/cds.cc",
        "src/core/load_balancing/xds/xds_channel_args.h",
        "src/core/load_balancing/xds/xds_cluster_impl.cc",
--- a/build_autogenerated.yaml
+++ b/build_autogenerated.yaml
@ -823,6 +823,7 @@ libs:
  - src/core/lib/channel/channelz_registry.h
  - src/core/lib/channel/connected_channel.h
  - src/core/lib/channel/context.h
+  - src/core/lib/channel/metrics.h
  - src/core/lib/channel/promise_based_filter.h
  - src/core/lib/channel/status_util.h
  - src/core/lib/channel/tcp_tracer.h
@ -1177,6 +1178,7 @@ libs:
  - src/core/load_balancing/subchannel_interface.h
  - src/core/load_balancing/subchannel_list.h
  - src/core/load_balancing/weighted_round_robin/static_stride_scheduler.h
+  - src/core/load_balancing/weighted_target/weighted_target.h
  - src/core/load_balancing/xds/xds_channel_args.h
  - src/core/load_balancing/xds/xds_override_host.h
  - src/core/resolver/dns/c_ares/dns_resolver_ares.h
@ -1665,6 +1667,7 @@ libs:
  - src/core/lib/channel/channelz.cc
  - src/core/lib/channel/channelz_registry.cc
  - src/core/lib/channel/connected_channel.cc
+  - src/core/lib/channel/metrics.cc
  - src/core/lib/channel/promise_based_filter.cc
  - src/core/lib/channel/server_call_tracer_filter.cc
  - src/core/lib/channel/status_util.cc
@ -2319,6 +2322,7 @@ libs:
  - src/core/lib/channel/channelz_registry.h
  - src/core/lib/channel/connected_channel.h
  - src/core/lib/channel/context.h
+  - src/core/lib/channel/metrics.h
  - src/core/lib/channel/promise_based_filter.h
  - src/core/lib/channel/status_util.h
  - src/core/lib/channel/tcp_tracer.h
@ -2636,6 +2640,7 @@ libs:
  - src/core/load_balancing/subchannel_interface.h
  - src/core/load_balancing/subchannel_list.h
  - src/core/load_balancing/weighted_round_robin/static_stride_scheduler.h
+  - src/core/load_balancing/weighted_target/weighted_target.h
  - src/core/resolver/dns/c_ares/dns_resolver_ares.h
  - src/core/resolver/dns/c_ares/grpc_ares_ev_driver.h
  - src/core/resolver/dns/c_ares/grpc_ares_wrapper.h
@ -2784,6 +2789,7 @@ libs:
  - src/core/lib/channel/channelz.cc
  - src/core/lib/channel/channelz_registry.cc
  - src/core/lib/channel/connected_channel.cc
+  - src/core/lib/channel/metrics.cc
  - src/core/lib/channel/promise_based_filter.cc
  - src/core/lib/channel/server_call_tracer_filter.cc
  - src/core/lib/channel/status_util.cc
@ -4393,6 +4399,7 @@ libs:
  - src/core/lib/channel/channelz_registry.h
  - src/core/lib/channel/connected_channel.h
  - src/core/lib/channel/context.h
+  - src/core/lib/channel/metrics.h
  - src/core/lib/channel/promise_based_filter.h
  - src/core/lib/channel/status_util.h
  - src/core/lib/channel/tcp_tracer.h
@ -4741,6 +4748,7 @@ libs:
  - src/core/lib/channel/channelz.cc
  - src/core/lib/channel/channelz_registry.cc
  - src/core/lib/channel/connected_channel.cc
+  - src/core/lib/channel/metrics.cc
  - src/core/lib/channel/promise_based_filter.cc
  - src/core/lib/channel/server_call_tracer_filter.cc
  - src/core/lib/channel/status_util.cc
@ -12714,10 +12722,10 @@ targets:
  build: test
  language: c++
  headers:
-  - src/core/lib/channel/metrics.h
+  - test/core/util/fake_stats_plugin.h
  src:
-  - src/core/lib/channel/metrics.cc
  - test/core/channel/metrics_test.cc
+  - test/core/util/fake_stats_plugin.cc
  deps:
  - gtest
  - grpc_test_util
@ -19564,9 +19572,11 @@ targets:
  gtest: true
  build: test
  language: c++
-  headers: []
+  headers:
+  - test/core/util/fake_stats_plugin.h
  src:
  - test/core/client_channel/lb_policy/weighted_round_robin_config_test.cc
+  - test/core/util/fake_stats_plugin.cc
  deps:
  - gtest
  - grpc_test_util
@ -19579,11 +19589,13 @@ targets:
  - test/core/client_channel/lb_policy/lb_policy_test_lib.h
  - test/core/event_engine/event_engine_test_utils.h
  - test/core/event_engine/fuzzing_event_engine/fuzzing_event_engine.h
+  - test/core/util/fake_stats_plugin.h
  src:
  - test/core/event_engine/fuzzing_event_engine/fuzzing_event_engine.proto
  - test/core/client_channel/lb_policy/weighted_round_robin_test.cc
  - test/core/event_engine/event_engine_test_utils.cc
  - test/core/event_engine/fuzzing_event_engine/fuzzing_event_engine.cc
+  - test/core/util/fake_stats_plugin.cc
  deps:
  - gtest
  - protobuf
@ -21224,6 +21236,7 @@ targets:
  build: test
  language: c++
  headers:
+  - test/core/util/fake_stats_plugin.h
  - test/core/util/scoped_env_var.h
  - test/cpp/end2end/counted_service.h
  - test/cpp/end2end/test_service_impl.h
@ -21265,6 +21278,7 @@ targets:
  - src/proto/grpc/testing/xds/v3/router.proto
  - src/proto/grpc/testing/xds/v3/string.proto
  - src/proto/grpc/testing/xds/v3/wrr_locality.proto
+  - test/core/util/fake_stats_plugin.cc
  - test/cpp/end2end/test_service_impl.cc
  - test/cpp/end2end/xds/xds_end2end_test_lib.cc
  - test/cpp/end2end/xds/xds_server.cc
--- a/config.m4
+++ b/config.m4
@ -474,6 +474,7 @@ if test "$PHP_GRPC" != "no"; then
    src/core/lib/channel/channelz.cc \
    src/core/lib/channel/channelz_registry.cc \
    src/core/lib/channel/connected_channel.cc \
+    src/core/lib/channel/metrics.cc \
    src/core/lib/channel/promise_based_filter.cc \
    src/core/lib/channel/server_call_tracer_filter.cc \
    src/core/lib/channel/status_util.cc \
--- a/config.w32
+++ b/config.w32
@ -439,6 +439,7 @@ if (PHP_GRPC != "no") {
    "src\\core\\lib\\channel\\channelz.cc " +
    "src\\core\\lib\\channel\\channelz_registry.cc " +
    "src\\core\\lib\\channel\\connected_channel.cc " +
+    "src\\core\\lib\\channel\\metrics.cc " +
    "src\\core\\lib\\channel\\promise_based_filter.cc " +
    "src\\core\\lib\\channel\\server_call_tracer_filter.cc " +
    "src\\core\\lib\\channel\\status_util.cc " +
--- a/gRPC-C++.podspec
+++ b/gRPC-C++.podspec
@ -903,6 +903,7 @@ Pod::Spec.new do |s|
                      'src/core/lib/channel/channelz_registry.h',
                      'src/core/lib/channel/connected_channel.h',
                      'src/core/lib/channel/context.h',
+                      'src/core/lib/channel/metrics.h',
                      'src/core/lib/channel/promise_based_filter.h',
                      'src/core/lib/channel/status_util.h',
                      'src/core/lib/channel/tcp_tracer.h',
@ -1282,6 +1283,7 @@ Pod::Spec.new do |s|
                      'src/core/load_balancing/subchannel_interface.h',
                      'src/core/load_balancing/subchannel_list.h',
                      'src/core/load_balancing/weighted_round_robin/static_stride_scheduler.h',
+                      'src/core/load_balancing/weighted_target/weighted_target.h',
                      'src/core/load_balancing/xds/xds_channel_args.h',
                      'src/core/load_balancing/xds/xds_override_host.h',
                      'src/core/resolver/dns/c_ares/dns_resolver_ares.h',
@ -2159,6 +2161,7 @@ Pod::Spec.new do |s|
                              'src/core/lib/channel/channelz_registry.h',
                              'src/core/lib/channel/connected_channel.h',
                              'src/core/lib/channel/context.h',
+                              'src/core/lib/channel/metrics.h',
                              'src/core/lib/channel/promise_based_filter.h',
                              'src/core/lib/channel/status_util.h',
                              'src/core/lib/channel/tcp_tracer.h',
@ -2538,6 +2541,7 @@ Pod::Spec.new do |s|
                              'src/core/load_balancing/subchannel_interface.h',
                              'src/core/load_balancing/subchannel_list.h',
                              'src/core/load_balancing/weighted_round_robin/static_stride_scheduler.h',
+                              'src/core/load_balancing/weighted_target/weighted_target.h',
                              'src/core/load_balancing/xds/xds_channel_args.h',
                              'src/core/load_balancing/xds/xds_override_host.h',
                              'src/core/resolver/dns/c_ares/dns_resolver_ares.h',
--- a/gRPC-Core.podspec
+++ b/gRPC-Core.podspec
@ -1268,6 +1268,8 @@ Pod::Spec.new do |s|
                      'src/core/lib/channel/connected_channel.cc',
                      'src/core/lib/channel/connected_channel.h',
                      'src/core/lib/channel/context.h',
+                      'src/core/lib/channel/metrics.cc',
+                      'src/core/lib/channel/metrics.h',
                      'src/core/lib/channel/promise_based_filter.cc',
                      'src/core/lib/channel/promise_based_filter.h',
                      'src/core/lib/channel/server_call_tracer_filter.cc',
@ -1999,6 +2001,7 @@ Pod::Spec.new do |s|
                      'src/core/load_balancing/weighted_round_robin/static_stride_scheduler.h',
                      'src/core/load_balancing/weighted_round_robin/weighted_round_robin.cc',
                      'src/core/load_balancing/weighted_target/weighted_target.cc',
+                      'src/core/load_balancing/weighted_target/weighted_target.h',
                      'src/core/load_balancing/xds/cds.cc',
                      'src/core/load_balancing/xds/xds_channel_args.h',
                      'src/core/load_balancing/xds/xds_cluster_impl.cc',
@ -2938,6 +2941,7 @@ Pod::Spec.new do |s|
                              'src/core/lib/channel/channelz_registry.h',
                              'src/core/lib/channel/connected_channel.h',
                              'src/core/lib/channel/context.h',
+                              'src/core/lib/channel/metrics.h',
                              'src/core/lib/channel/promise_based_filter.h',
                              'src/core/lib/channel/status_util.h',
                              'src/core/lib/channel/tcp_tracer.h',
@ -3317,6 +3321,7 @@ Pod::Spec.new do |s|
                              'src/core/load_balancing/subchannel_interface.h',
                              'src/core/load_balancing/subchannel_list.h',
                              'src/core/load_balancing/weighted_round_robin/static_stride_scheduler.h',
+                              'src/core/load_balancing/weighted_target/weighted_target.h',
                              'src/core/load_balancing/xds/xds_channel_args.h',
                              'src/core/load_balancing/xds/xds_override_host.h',
                              'src/core/resolver/dns/c_ares/dns_resolver_ares.h',
--- a/grpc.gemspec
+++ b/grpc.gemspec
@ -1161,6 +1161,8 @@ Gem::Specification.new do |s|
  s.files += %w( src/core/lib/channel/connected_channel.cc )
  s.files += %w( src/core/lib/channel/connected_channel.h )
  s.files += %w( src/core/lib/channel/context.h )
+  s.files += %w( src/core/lib/channel/metrics.cc )
+  s.files += %w( src/core/lib/channel/metrics.h )
  s.files += %w( src/core/lib/channel/promise_based_filter.cc )
  s.files += %w( src/core/lib/channel/promise_based_filter.h )
  s.files += %w( src/core/lib/channel/server_call_tracer_filter.cc )
@ -1892,6 +1894,7 @@ Gem::Specification.new do |s|
  s.files += %w( src/core/load_balancing/weighted_round_robin/static_stride_scheduler.h )
  s.files += %w( src/core/load_balancing/weighted_round_robin/weighted_round_robin.cc )
  s.files += %w( src/core/load_balancing/weighted_target/weighted_target.cc )
+  s.files += %w( src/core/load_balancing/weighted_target/weighted_target.h )
  s.files += %w( src/core/load_balancing/xds/cds.cc )
  s.files += %w( src/core/load_balancing/xds/xds_channel_args.h )
  s.files += %w( src/core/load_balancing/xds/xds_cluster_impl.cc )
--- a/grpc.gyp
+++ b/grpc.gyp
@ -705,6 +705,7 @@
        'src/core/lib/channel/channelz.cc',
        'src/core/lib/channel/channelz_registry.cc',
        'src/core/lib/channel/connected_channel.cc',
+        'src/core/lib/channel/metrics.cc',
        'src/core/lib/channel/promise_based_filter.cc',
        'src/core/lib/channel/server_call_tracer_filter.cc',
        'src/core/lib/channel/status_util.cc',
@ -1246,6 +1247,7 @@
        'src/core/lib/channel/channelz.cc',
        'src/core/lib/channel/channelz_registry.cc',
        'src/core/lib/channel/connected_channel.cc',
+        'src/core/lib/channel/metrics.cc',
        'src/core/lib/channel/promise_based_filter.cc',
        'src/core/lib/channel/server_call_tracer_filter.cc',
        'src/core/lib/channel/status_util.cc',
@ -2054,6 +2056,7 @@
        'src/core/lib/channel/channelz.cc',
        'src/core/lib/channel/channelz_registry.cc',
        'src/core/lib/channel/connected_channel.cc',
+        'src/core/lib/channel/metrics.cc',
        'src/core/lib/channel/promise_based_filter.cc',
        'src/core/lib/channel/server_call_tracer_filter.cc',
        'src/core/lib/channel/status_util.cc',
--- a/package.xml
+++ b/package.xml
@ -1143,6 +1143,8 @@
    <file baseinstalldir="/" name="src/core/lib/channel/connected_channel.cc" role="src" />
    <file baseinstalldir="/" name="src/core/lib/channel/connected_channel.h" role="src" />
    <file baseinstalldir="/" name="src/core/lib/channel/context.h" role="src" />
+    <file baseinstalldir="/" name="src/core/lib/channel/metrics.cc" role="src" />
+    <file baseinstalldir="/" name="src/core/lib/channel/metrics.h" role="src" />
    <file baseinstalldir="/" name="src/core/lib/channel/promise_based_filter.cc" role="src" />
    <file baseinstalldir="/" name="src/core/lib/channel/promise_based_filter.h" role="src" />
    <file baseinstalldir="/" name="src/core/lib/channel/server_call_tracer_filter.cc" role="src" />
@ -1874,6 +1876,7 @@
    <file baseinstalldir="/" name="src/core/load_balancing/weighted_round_robin/static_stride_scheduler.h" role="src" />
    <file baseinstalldir="/" name="src/core/load_balancing/weighted_round_robin/weighted_round_robin.cc" role="src" />
    <file baseinstalldir="/" name="src/core/load_balancing/weighted_target/weighted_target.cc" role="src" />
+    <file baseinstalldir="/" name="src/core/load_balancing/weighted_target/weighted_target.h" role="src" />
    <file baseinstalldir="/" name="src/core/load_balancing/xds/cds.cc" role="src" />
    <file baseinstalldir="/" name="src/core/load_balancing/xds/xds_channel_args.h" role="src" />
    <file baseinstalldir="/" name="src/core/load_balancing/xds/xds_cluster_impl.cc" role="src" />
--- a/src/core/BUILD
+++ b/src/core/BUILD
@ -3256,6 +3256,7 @@ grpc_cc_library(
        "error",
        "grpc_backend_metric_data",
        "iomgr_fwd",
+        "metrics",
        "pollset_set",
        "ref_counted",
        "resolved_address",
@ -5680,6 +5681,7 @@ grpc_cc_library(
        "connectivity_state",
        "experiments",
        "grpc_backend_metric_data",
+        "grpc_lb_policy_weighted_target",
        "grpc_lb_subchannel_list",
        "json",
        "json_args",
@ -5687,6 +5689,7 @@ grpc_cc_library(
        "lb_endpoint_list",
        "lb_policy",
        "lb_policy_factory",
+        "metrics",
        "ref_counted",
        "resolved_address",
        "static_stride_scheduler",
@ -5826,6 +5829,9 @@ grpc_cc_library(
    srcs = [
        "load_balancing/weighted_target/weighted_target.cc",
    ],
+    hdrs = [
+        "load_balancing/weighted_target/weighted_target.h",
+    ],
    external_deps = [
        "absl/base:core_headers",
        "absl/meta:type_traits",
--- a/src/core/client_channel/client_channel_filter.cc
+++ b/src/core/client_channel/client_channel_filter.cc
@ -1148,6 +1148,8 @@ class ClientChannelFilter::ClientChannelControlHelper
    chand_->resolver_->RequestReresolutionLocked();
  }

+  absl::string_view GetTarget() override { return chand_->target_uri_; }
+
  absl::string_view GetAuthority() override {
    return chand_->default_authority_;
  }
@ -1166,6 +1168,10 @@ class ClientChannelFilter::ClientChannelControlHelper
    return chand_->owning_stack_->EventEngine();
  }

+  GlobalStatsPluginRegistry::StatsPluginGroup& GetStatsPluginGroup() override {
+    return *chand_->owning_stack_->stats_plugin_group;
+  }
+
  void AddTraceEvent(TraceSeverity severity, absl::string_view message) override
      ABSL_EXCLUSIVE_LOCKS_REQUIRED(*chand_->work_serializer_) {
    if (chand_->resolver_ == nullptr) return;  // Shutting down.
@ -1270,18 +1276,19 @@ ClientChannelFilter::ClientChannelFilter(grpc_channel_element_args* args,
  }
  default_service_config_ = std::move(*service_config);
  // Get URI to resolve, using proxy mapper if needed.
-  absl::optional<std::string> server_uri =
+  absl::optional<std::string> target_uri =
      channel_args_.GetOwnedString(GRPC_ARG_SERVER_URI);
-  if (!server_uri.has_value()) {
+  if (!target_uri.has_value()) {
    *error = GRPC_ERROR_CREATE(
        "target URI channel arg missing or wrong type in client channel "
        "filter");
    return;
  }
+  target_uri_ = std::move(*target_uri);
  uri_to_resolve_ = CoreConfiguration::Get()
                        .proxy_mapper_registry()
-                        .MapName(*server_uri, &channel_args_)
-                        .value_or(*server_uri);
+                        .MapName(target_uri_, &channel_args_)
+                        .value_or(target_uri_);
  // Make sure the URI to resolve is valid, so that we know that
  // resolver creation will succeed later.
  if (!CoreConfiguration::Get().resolver_registry().IsValidTarget(
@ -1306,7 +1313,7 @@ ClientChannelFilter::ClientChannelFilter(grpc_channel_element_args* args,
  if (!default_authority.has_value()) {
    default_authority_ =
        CoreConfiguration::Get().resolver_registry().GetDefaultAuthority(
-            *server_uri);
+            target_uri_);
  } else {
    default_authority_ = std::move(*default_authority);
  }
--- a/src/core/client_channel/client_channel_filter.h
+++ b/src/core/client_channel/client_channel_filter.h
@ -295,6 +295,7 @@ class ClientChannelFilter {
  grpc_channel_stack* owning_stack_;
  ClientChannelFactory* client_channel_factory_;
  RefCountedPtr<ServiceConfig> default_service_config_;
+  std::string target_uri_;
  std::string uri_to_resolve_;
  std::string default_authority_;
  channelz::ChannelNode* channelz_node_;
--- a/src/core/lib/channel/channel_stack.cc
+++ b/src/core/lib/channel/channel_stack.cc
@ -129,6 +129,7 @@ grpc_error_handle grpc_channel_stack_init(

  stack->on_destroy.Init([]() {});
  stack->event_engine.Init(channel_args.GetObjectRef<EventEngine>());
+  stack->stats_plugin_group.Init();

  size_t call_size =
      GPR_ROUND_UP_TO_ALIGNMENT_SIZE(sizeof(grpc_call_stack)) +
@ -188,6 +189,7 @@ void grpc_channel_stack_destroy(grpc_channel_stack* stack) {
  (*stack->on_destroy)();
  stack->on_destroy.Destroy();
  stack->event_engine.Destroy();
+  stack->stats_plugin_group.Destroy();
 }

 grpc_error_handle grpc_call_stack_init(
--- a/src/core/lib/channel/channel_stack.h
+++ b/src/core/lib/channel/channel_stack.h
@ -61,6 +61,7 @@
 #include "src/core/lib/channel/channel_args.h"
 #include "src/core/lib/channel/channel_fwd.h"
 #include "src/core/lib/channel/context.h"
+#include "src/core/lib/channel/metrics.h"
 #include "src/core/lib/debug/trace.h"
 #include "src/core/lib/gpr/time_precise.h"
 #include "src/core/lib/gprpp/manual_constructor.h"
@ -219,6 +220,10 @@ struct grpc_channel_stack {
    return event_engine->get();
  }

+  grpc_core::ManualConstructor<
+      grpc_core::GlobalStatsPluginRegistry::StatsPluginGroup>
+      stats_plugin_group;
+
  // Minimal infrastructure to act like a RefCounted thing without converting
  // everything.
  // It's likely that we'll want to replace grpc_channel_stack with something
--- a/src/core/lib/channel/metrics.cc
+++ b/src/core/lib/channel/metrics.cc
@ -21,18 +21,17 @@
 #include "src/core/lib/gprpp/crash.h"

 namespace grpc_core {
-namespace {
+
 // Uses the Construct-on-First-Use idiom to avoid the static initialization
 // order fiasco.
 absl::flat_hash_map<absl::string_view,
                    GlobalInstrumentsRegistry::GlobalInstrumentDescriptor>&
-GetInstrumentList() {
+GlobalInstrumentsRegistry::GetInstrumentList() {
  static NoDestruct<absl::flat_hash_map<
      absl::string_view, GlobalInstrumentsRegistry::GlobalInstrumentDescriptor>>
      instruments;
  return *instruments;
 }
-}  // namespace

 GlobalInstrumentsRegistry::GlobalUInt64CounterHandle
 GlobalInstrumentsRegistry::RegisterUInt64Counter(
@ -157,11 +156,6 @@ void GlobalInstrumentsRegistry::ForEach(
  }
 }

-void GlobalInstrumentsRegistry::TestOnlyResetGlobalInstrumentsRegistry() {
-  auto& instruments = GetInstrumentList();
-  instruments.clear();
-}
-
 NoDestruct<Mutex> GlobalStatsPluginRegistry::mutex_;
 NoDestruct<std::vector<std::shared_ptr<StatsPlugin>>>
    GlobalStatsPluginRegistry::plugins_;
--- a/src/core/lib/channel/metrics.h
+++ b/src/core/lib/channel/metrics.h
@ -21,6 +21,7 @@
 #include <memory>
 #include <vector>

+#include "absl/container/flat_hash_map.h"
 #include "absl/functional/function_ref.h"
 #include "absl/strings/string_view.h"
 #include "absl/types/span.h"
@ -33,6 +34,8 @@

 namespace grpc_core {

+constexpr absl::string_view kMetricLabelTarget = "grpc.target";
+
 // A global registry of instruments(metrics). This API is designed to be used to
 // register instruments (Counter and Histogram) as part of program startup,
 // before the execution of the main function (during dynamic initialization
@ -97,9 +100,14 @@ class GlobalInstrumentsRegistry {
  static void ForEach(
      absl::FunctionRef<void(const GlobalInstrumentDescriptor&)> f);

-  static void TestOnlyResetGlobalInstrumentsRegistry();
+ private:
+  friend class GlobalInstrumentsRegistryTestPeer;

  GlobalInstrumentsRegistry() = delete;
+
+  static absl::flat_hash_map<
+      absl::string_view, GlobalInstrumentsRegistry::GlobalInstrumentDescriptor>&
+  GetInstrumentList();
 };

 // The StatsPlugin interface.
@ -213,12 +221,9 @@ class GlobalStatsPluginRegistry {
  // TODO(yijiem): Implement this.
  // StatsPluginsGroup GetStatsPluginsForServer(ChannelArgs& args);

-  static void TestOnlyResetGlobalStatsPluginRegistry() {
-    MutexLock lock(&*mutex_);
-    plugins_->clear();
-  }
-
 private:
+  friend class GlobalStatsPluginRegistryTestPeer;
+
  GlobalStatsPluginRegistry() = default;

  static NoDestruct<Mutex> mutex_;
--- a/src/core/lib/surface/channel.cc
+++ b/src/core/lib/surface/channel.cc
@ -42,6 +42,7 @@
 #include "src/core/lib/channel/channel_stack_builder_impl.h"
 #include "src/core/lib/channel/channel_trace.h"
 #include "src/core/lib/channel/channelz.h"
+#include "src/core/lib/channel/metrics.h"
 #include "src/core/lib/config/core_configuration.h"
 #include "src/core/lib/debug/stats.h"
 #include "src/core/lib/debug/stats_data.h"
@ -160,6 +161,12 @@ absl::StatusOr<RefCountedPtr<Channel>> Channel::CreateWithBuilder(
        *enabled_algorithms_bitset | 1 /* always support no compression */;
  }

+  // TODO(roth): Populate authority after merging
+  // https://github.com/grpc/grpc/pull/35924.
+  StatsPlugin::ChannelScope scope(builder->target(), "");
+  *(*r)->stats_plugin_group =
+      GlobalStatsPluginRegistry::GetStatsPluginsForChannel(scope);
+
  return RefCountedPtr<Channel>(new Channel(
      grpc_channel_stack_type_is_client(builder->channel_stack_type()),
      builder->IsPromising(), std::string(builder->target()), channel_args,
--- a/src/core/load_balancing/delegating_helper.h
+++ b/src/core/load_balancing/delegating_helper.h
@ -58,6 +58,10 @@ class LoadBalancingPolicy::DelegatingChannelControlHelper
    parent_helper()->RequestReresolution();
  }

+  absl::string_view GetTarget() override {
+    return parent_helper()->GetTarget();
+  }
+
  absl::string_view GetAuthority() override {
    return parent_helper()->GetAuthority();
  }
@ -75,6 +79,10 @@ class LoadBalancingPolicy::DelegatingChannelControlHelper
    return parent_helper()->GetEventEngine();
  }

+  GlobalStatsPluginRegistry::StatsPluginGroup& GetStatsPluginGroup() override {
+    return parent_helper()->GetStatsPluginGroup();
+  }
+
  void AddTraceEvent(TraceSeverity severity,
                     absl::string_view message) override {
    parent_helper()->AddTraceEvent(severity, message);
--- a/src/core/load_balancing/lb_policy.h
+++ b/src/core/load_balancing/lb_policy.h
@ -40,6 +40,7 @@

 #include "src/core/load_balancing/backend_metric_data.h"
 #include "src/core/lib/channel/channel_args.h"
+#include "src/core/lib/channel/metrics.h"
 #include "src/core/lib/debug/trace.h"
 #include "src/core/lib/gprpp/debug_location.h"
 #include "src/core/lib/gprpp/dual_ref_counted.h"
@ -299,6 +300,9 @@ class LoadBalancingPolicy : public InternallyRefCounted<LoadBalancingPolicy> {
    /// Requests that the resolver re-resolve.
    virtual void RequestReresolution() = 0;

+    /// Returns the channel target.
+    virtual absl::string_view GetTarget() = 0;
+
    /// Returns the channel authority.
    virtual absl::string_view GetAuthority() = 0;

@ -319,6 +323,10 @@ class LoadBalancingPolicy : public InternallyRefCounted<LoadBalancingPolicy> {
    /// Returns the EventEngine to use for timers and async work.
    virtual grpc_event_engine::experimental::EventEngine* GetEventEngine() = 0;

+    /// Returns the stats plugin group for reporting metrics.
+    virtual GlobalStatsPluginRegistry::StatsPluginGroup&
+    GetStatsPluginGroup() = 0;
+
    /// Adds a trace message associated with the channel.
    enum TraceSeverity { TRACE_INFO, TRACE_WARNING, TRACE_ERROR };
    virtual void AddTraceEvent(TraceSeverity severity,
--- a/src/core/load_balancing/weighted_round_robin/weighted_round_robin.cc
+++ b/src/core/load_balancing/weighted_round_robin/weighted_round_robin.cc
@ -51,8 +51,10 @@
 #include "src/core/load_balancing/oob_backend_metric.h"
 #include "src/core/load_balancing/subchannel_list.h"
 #include "src/core/load_balancing/weighted_round_robin/static_stride_scheduler.h"
+#include "src/core/load_balancing/weighted_target/weighted_target.h"
 #include "src/core/lib/address_utils/sockaddr_utils.h"
 #include "src/core/lib/channel/channel_args.h"
+#include "src/core/lib/channel/metrics.h"
 #include "src/core/lib/config/core_configuration.h"
 #include "src/core/lib/debug/stats.h"
 #include "src/core/lib/debug/stats_data.h"
@ -86,6 +88,41 @@ namespace {

 constexpr absl::string_view kWeightedRoundRobin = "weighted_round_robin";

+constexpr absl::string_view kMetricLabelLocality = "grpc.lb.locality";
+
+const auto kMetricRrFallback =
+    GlobalInstrumentsRegistry::RegisterUInt64Counter(
+        "grpc.lb.wrr.rr_fallback",
+        "EXPERIMENTAL.  Number of scheduler updates in which there were not "
+        "enough endpoints with valid weight, which caused the WRR policy to "
+        "fall back to RR behavior.",
+        "{update}", {kMetricLabelTarget}, {kMetricLabelLocality}, false);
+
+const auto kMetricEndpointWeightNotYetUsable =
+    GlobalInstrumentsRegistry::RegisterUInt64Counter(
+        "grpc.lb.wrr.endpoint_weight_not_yet_usable",
+        "EXPERIMENTAL.  Number of endpoints from each scheduler update that "
+        "don't yet have usable weight information (i.e., either the load "
+        "report has not yet been received, or it is within the blackout "
+        "period).",
+        "{endpoint}", {kMetricLabelTarget}, {kMetricLabelLocality}, false);
+
+const auto kMetricEndpointWeightStale =
+    GlobalInstrumentsRegistry::RegisterUInt64Counter(
+        "grpc.lb.wrr.endpoint_weight_stale",
+        "EXPERIMENTAL.  Number of endpoints from each scheduler update whose "
+        "latest weight is older than the expiration period.",
+        "{endpoint}", {kMetricLabelTarget}, {kMetricLabelLocality}, false);
+
+const auto kMetricEndpointWeights =
+    GlobalInstrumentsRegistry::RegisterDoubleHistogram(
+        "grpc.lb.wrr.endpoint_weights",
+        "EXPERIMENTAL.  The histogram buckets will be endpoint weight ranges.  "
+        "Each bucket will be a counter that is incremented once for every "
+        "endpoint whose weight is within that range. Note that endpoints "
+        "without usable weights will have weight 0.",
+        "{weight}", {kMetricLabelTarget}, {kMetricLabelLocality}, false);
+
 // Config for WRR policy.
 class WeightedRoundRobinConfig : public LoadBalancingPolicy::Config {
 public:
@ -1021,7 +1058,8 @@ class WeightedRoundRobin : public LoadBalancingPolicy {
                           float error_utilization_penalty);

    float GetWeight(Timestamp now, Duration weight_expiration_period,
-                    Duration blackout_period);
+                    Duration blackout_period, uint64_t* num_not_yet_usable,
+                    uint64_t* num_stale);

    void ResetNonEmptySince();

@ -1215,6 +1253,8 @@ class WeightedRoundRobin : public LoadBalancingPolicy {
  std::map<EndpointAddressSet, EndpointWeight*> endpoint_weight_map_
      ABSL_GUARDED_BY(&endpoint_weight_map_mu_);

+  const absl::string_view locality_name_;
+
  bool shutdown_ = false;

  absl::BitGen bit_gen_;
@ -1276,8 +1316,8 @@ void WeightedRoundRobin::EndpointWeight::MaybeUpdateWeight(
 }

 float WeightedRoundRobin::EndpointWeight::GetWeight(
-    Timestamp now, Duration weight_expiration_period,
-    Duration blackout_period) {
+    Timestamp now, Duration weight_expiration_period, Duration blackout_period,
+    uint64_t* num_not_yet_usable, uint64_t* num_stale) {
  MutexLock lock(&mu_);
  if (GRPC_TRACE_FLAG_ENABLED(grpc_lb_wrr_trace)) {
    gpr_log(GPR_INFO,
@ -1294,12 +1334,14 @@ float WeightedRoundRobin::EndpointWeight::GetWeight(
  // period, reset non_empty_since_ so that we apply the blackout period
  // again if we start getting data again in the future, and return 0.
  if (now - last_update_time_ >= weight_expiration_period) {
+    ++*num_stale;
    non_empty_since_ = Timestamp::InfFuture();
    return 0;
  }
  // If we don't have at least blackout_period worth of data, return 0.
  if (blackout_period > Duration::Zero() &&
      now - non_empty_since_ < blackout_period) {
+    ++*num_not_yet_usable;
    return 0;
  }
  // Otherwise, return the weight.
@ -1418,14 +1460,28 @@ size_t WeightedRoundRobin::Picker::PickIndex() {
 }

 void WeightedRoundRobin::Picker::BuildSchedulerAndStartTimerLocked() {
-  // Build scheduler.
+  auto& stats_plugins = wrr_->channel_control_helper()->GetStatsPluginGroup();
+  // Build scheduler, reporting metrics on endpoint weights.
  const Timestamp now = Timestamp::Now();
  std::vector<float> weights;
  weights.reserve(endpoints_.size());
+  uint64_t num_not_yet_usable = 0;
+  uint64_t num_stale = 0;
  for (const auto& endpoint : endpoints_) {
-    weights.push_back(endpoint.weight->GetWeight(
-        now, config_->weight_expiration_period(), config_->blackout_period()));
+    float weight = endpoint.weight->GetWeight(
+        now, config_->weight_expiration_period(), config_->blackout_period(),
+        &num_not_yet_usable, &num_stale);
+    weights.push_back(weight);
+    stats_plugins.RecordHistogram(
+        kMetricEndpointWeights, weight,
+        {wrr_->channel_control_helper()->GetTarget()}, {wrr_->locality_name_});
  }
+  stats_plugins.AddCounter(
+      kMetricEndpointWeightNotYetUsable, num_not_yet_usable,
+      {wrr_->channel_control_helper()->GetTarget()}, {wrr_->locality_name_});
+  stats_plugins.AddCounter(
+      kMetricEndpointWeightStale, num_stale,
+      {wrr_->channel_control_helper()->GetTarget()}, {wrr_->locality_name_});
  if (GRPC_TRACE_FLAG_ENABLED(grpc_lb_wrr_trace)) {
    gpr_log(GPR_INFO, "[WRR %p picker %p] new weights: %s", wrr_.get(), this,
            absl::StrJoin(weights, " ").c_str());
@ -1440,9 +1496,14 @@ void WeightedRoundRobin::Picker::BuildSchedulerAndStartTimerLocked() {
      gpr_log(GPR_INFO, "[WRR %p picker %p] new scheduler: %p", wrr_.get(),
              this, scheduler.get());
    }
-  } else if (GRPC_TRACE_FLAG_ENABLED(grpc_lb_wrr_trace)) {
-    gpr_log(GPR_INFO, "[WRR %p picker %p] no scheduler, falling back to RR",
-            wrr_.get(), this);
+  } else {
+    if (GRPC_TRACE_FLAG_ENABLED(grpc_lb_wrr_trace)) {
+      gpr_log(GPR_INFO, "[WRR %p picker %p] no scheduler, falling back to RR",
+              wrr_.get(), this);
+    }
+    stats_plugins.AddCounter(
+        kMetricRrFallback, 1, {wrr_->channel_control_helper()->GetTarget()},
+        {wrr_->locality_name_});
  }
  {
    MutexLock lock(&scheduler_mu_);
@ -1483,9 +1544,13 @@ void WeightedRoundRobin::Picker::BuildSchedulerAndStartTimerLocked() {
 //

 WeightedRoundRobin::WeightedRoundRobin(Args args)
-    : LoadBalancingPolicy(std::move(args)) {
+    : LoadBalancingPolicy(std::move(args)),
+      locality_name_(channel_args()
+                         .GetString(GRPC_ARG_LB_WEIGHTED_TARGET_CHILD)
+                         .value_or("")) {
  if (GRPC_TRACE_FLAG_ENABLED(grpc_lb_wrr_trace)) {
-    gpr_log(GPR_INFO, "[WRR %p] Created", this);
+    gpr_log(GPR_INFO, "[WRR %p] Created -- locality_name=\"%s\"", this,
+            std::string(locality_name_).c_str());
  }
 }

--- a/src/core/load_balancing/weighted_target/weighted_target.cc
+++ b/src/core/load_balancing/weighted_target/weighted_target.cc
@ -16,6 +16,8 @@

 #include <grpc/support/port_platform.h>

+#include "src/core/load_balancing/weighted_target/weighted_target.h"
+
 #include <string.h>

 #include <algorithm>
@ -160,7 +162,7 @@ class WeightedTargetLb : public LoadBalancingPolicy {
    absl::Status UpdateLocked(
        const WeightedTargetLbConfig::ChildConfig& config,
        absl::StatusOr<std::shared_ptr<EndpointAddressesIterator>> addresses,
-        const std::string& resolution_note, const ChannelArgs& args);
+        const std::string& resolution_note, ChannelArgs args);
    void ResetBackoffLocked();
    void DeactivateLocked();

@ -592,7 +594,7 @@ WeightedTargetLb::WeightedChild::CreateChildPolicyLocked(
 absl::Status WeightedTargetLb::WeightedChild::UpdateLocked(
    const WeightedTargetLbConfig::ChildConfig& config,
    absl::StatusOr<std::shared_ptr<EndpointAddressesIterator>> addresses,
-    const std::string& resolution_note, const ChannelArgs& args) {
+    const std::string& resolution_note, ChannelArgs args) {
  if (weighted_target_policy_->shutting_down_) return absl::OkStatus();
  // Update child weight.
  if (weight_ != config.weight &&
@ -611,6 +613,7 @@ absl::Status WeightedTargetLb::WeightedChild::UpdateLocked(
    delayed_removal_timer_.reset();
  }
  // Create child policy if needed.
+  args = args.Set(GRPC_ARG_LB_WEIGHTED_TARGET_CHILD, name_);
  if (child_policy_ == nullptr) {
    child_policy_ = CreateChildPolicyLocked(args);
  }
@ -619,7 +622,7 @@ absl::Status WeightedTargetLb::WeightedChild::UpdateLocked(
  update_args.config = config.config;
  update_args.addresses = std::move(addresses);
  update_args.resolution_note = resolution_note;
-  update_args.args = args;
+  update_args.args = std::move(args);
  // Update the policy.
  if (GRPC_TRACE_FLAG_ENABLED(grpc_lb_weighted_target_trace)) {
    gpr_log(GPR_INFO,
--- a/src/core/load_balancing/weighted_target/weighted_target.h
+++ b/src/core/load_balancing/weighted_target/weighted_target.h
@ -0,0 +1,28 @@
+//
+// Copyright 2024 gRPC authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+
+#ifndef GRPC_SRC_CORE_LOAD_BALANCING_WEIGHTED_TARGET_WEIGHTED_TARGET_H
+#define GRPC_SRC_CORE_LOAD_BALANCING_WEIGHTED_TARGET_WEIGHTED_TARGET_H
+
+#include <grpc/support/port_platform.h>
+
+#include "src/core/resolver/endpoint_addresses.h"
+
+// Channel arg key indicating the weighted_target child name.
+#define GRPC_ARG_LB_WEIGHTED_TARGET_CHILD \
+   GRPC_ARG_NO_SUBCHANNEL_PREFIX "lb_weighted_target_child"
+
+#endif  // GRPC_SRC_CORE_LOAD_BALANCING_WEIGHTED_TARGET_WEIGHTED_TARGET_H
--- a/src/python/grpcio/grpc_core_dependencies.py
+++ b/src/python/grpcio/grpc_core_dependencies.py
@ -448,6 +448,7 @@ CORE_SOURCE_FILES = [
    'src/core/lib/channel/channelz.cc',
    'src/core/lib/channel/channelz_registry.cc',
    'src/core/lib/channel/connected_channel.cc',
+    'src/core/lib/channel/metrics.cc',
    'src/core/lib/channel/promise_based_filter.cc',
    'src/core/lib/channel/server_call_tracer_filter.cc',
    'src/core/lib/channel/status_util.cc',
--- a/test/core/channel/BUILD
+++ b/test/core/channel/BUILD
@ -204,6 +204,7 @@ grpc_cc_test(
    uses_polling = False,
    deps = [
        "//src/core:metrics",
+        "//test/core/util:fake_stats_plugin",
        "//test/core/util:grpc_test_util",
    ],
 )
--- a/test/core/channel/metrics_test.cc
+++ b/test/core/channel/metrics_test.cc
@ -23,299 +23,17 @@
 #include "gmock/gmock.h"
 #include "gtest/gtest.h"

+#include "test/core/util/fake_stats_plugin.h"
 #include "test/core/util/test_config.h"

 namespace grpc_core {
 namespace {

-void AddKeyValuePairs(absl::Span<const absl::string_view> keys,
-                      absl::Span<const absl::string_view> values,
-                      std::vector<std::string>* key_value_pairs) {
-  GPR_ASSERT(keys.size() == values.size());
-  for (size_t i = 0; i < keys.size(); ++i) {
-    key_value_pairs->push_back(absl::StrCat(keys[i], "=", values[i]));
-  }
-}
-
-std::string MakeLabelString(
-    absl::Span<const absl::string_view> label_keys,
-    absl::Span<const absl::string_view> label_values,
-    absl::Span<const absl::string_view> optional_label_keys,
-    absl::Span<const absl::string_view> optional_values) {
-  std::vector<std::string> key_value_pairs;
-  AddKeyValuePairs(label_keys, label_values, &key_value_pairs);
-  AddKeyValuePairs(optional_label_keys, optional_values, &key_value_pairs);
-  return absl::StrJoin(key_value_pairs, ",");
-}
-
-// TODO(yijiem): Move this to test/core/util/fake_stats_plugin.h
-class FakeStatsPlugin : public StatsPlugin {
- public:
-  bool IsEnabledForChannel(
-      const StatsPlugin::ChannelScope& scope) const override {
-    return channel_filter_(scope);
-  }
-
-  bool IsEnabledForServer(const ChannelArgs& /*args*/) const override {
-    return false;
-  }
-
-  void AddCounter(
-      GlobalInstrumentsRegistry::GlobalUInt64CounterHandle handle,
-      uint64_t value, absl::Span<const absl::string_view> label_values,
-      absl::Span<const absl::string_view> optional_values) override {
-    // The problem with this approach is that we initialize uint64_counters_ in
-    // BuildAndRegister by querying the GlobalInstrumentsRegistry at the time.
-    // If the GlobalInstrumentsRegistry has changed since then (which we
-    // currently don't allow), we might not have seen that descriptor nor have
-    // we created an instrument for it. We probably could copy the existing
-    // instruments at build time and for the handle that we haven't seen we will
-    // just ignore it here. This would also prevent us from having to lock the
-    // GlobalInstrumentsRegistry everytime a metric is recorded. But this is not
-    // a concern for now.
-    auto iter = uint64_counters_.find(handle.index);
-    if (iter == uint64_counters_.end()) {
-      return;
-    }
-    iter->second.Add(value, label_values, optional_values);
-  }
-  void AddCounter(
-      GlobalInstrumentsRegistry::GlobalDoubleCounterHandle handle, double value,
-      absl::Span<const absl::string_view> label_values,
-      absl::Span<const absl::string_view> optional_values) override {
-    auto iter = double_counters_.find(handle.index);
-    if (iter == double_counters_.end()) {
-      return;
-    }
-    iter->second.Add(value, label_values, optional_values);
-  }
-  void RecordHistogram(
-      GlobalInstrumentsRegistry::GlobalUInt64HistogramHandle handle,
-      uint64_t value, absl::Span<const absl::string_view> label_values,
-      absl::Span<const absl::string_view> optional_values) override {
-    auto iter = uint64_histograms_.find(handle.index);
-    if (iter == uint64_histograms_.end()) {
-      return;
-    }
-    iter->second.Record(value, label_values, optional_values);
-  }
-  void RecordHistogram(
-      GlobalInstrumentsRegistry::GlobalDoubleHistogramHandle handle,
-      double value, absl::Span<const absl::string_view> label_values,
-      absl::Span<const absl::string_view> optional_values) override {
-    auto iter = double_histograms_.find(handle.index);
-    if (iter == double_histograms_.end()) {
-      return;
-    }
-    iter->second.Record(value, label_values, optional_values);
-  }
-
-  absl::optional<uint64_t> GetCounterValue(
-      GlobalInstrumentsRegistry::GlobalUInt64CounterHandle handle,
-      absl::Span<const absl::string_view> label_values,
-      absl::Span<const absl::string_view> optional_values) {
-    auto iter = uint64_counters_.find(handle.index);
-    if (iter == uint64_counters_.end()) {
-      return absl::nullopt;
-    }
-    return iter->second.GetValue(label_values, optional_values);
-  }
-  absl::optional<double> GetCounterValue(
-      GlobalInstrumentsRegistry::GlobalDoubleCounterHandle handle,
-      absl::Span<const absl::string_view> label_values,
-      absl::Span<const absl::string_view> optional_values) {
-    auto iter = double_counters_.find(handle.index);
-    if (iter == double_counters_.end()) {
-      return absl::nullopt;
-    }
-    return iter->second.GetValue(label_values, optional_values);
-  }
-  absl::optional<std::vector<uint64_t>> GetHistogramValue(
-      GlobalInstrumentsRegistry::GlobalUInt64HistogramHandle handle,
-      absl::Span<const absl::string_view> label_values,
-      absl::Span<const absl::string_view> optional_values) {
-    auto iter = uint64_histograms_.find(handle.index);
-    if (iter == uint64_histograms_.end()) {
-      return absl::nullopt;
-    }
-    return iter->second.GetValues(label_values, optional_values);
-  }
-  absl::optional<std::vector<double>> GetHistogramValue(
-      GlobalInstrumentsRegistry::GlobalDoubleHistogramHandle handle,
-      absl::Span<const absl::string_view> label_values,
-      absl::Span<const absl::string_view> optional_values) {
-    auto iter = double_histograms_.find(handle.index);
-    if (iter == double_histograms_.end()) {
-      return absl::nullopt;
-    }
-    return iter->second.GetValues(label_values, optional_values);
-  }
-
- private:
-  friend class FakeStatsPluginBuilder;
-
-  explicit FakeStatsPlugin(
-      absl::AnyInvocable<bool(const StatsPlugin::ChannelScope& /*scope*/) const>
-          channel_filter)
-      : channel_filter_(std::move(channel_filter)) {
-    GlobalInstrumentsRegistry::ForEach(
-        [this](const GlobalInstrumentsRegistry::GlobalInstrumentDescriptor&
-                   descriptor) {
-          if (!descriptor.enable_by_default) {
-            return;
-          }
-          if (descriptor.instrument_type ==
-              GlobalInstrumentsRegistry::InstrumentType::kCounter) {
-            if (descriptor.value_type ==
-                GlobalInstrumentsRegistry::ValueType::kUInt64) {
-              uint64_counters_.emplace(descriptor.index, descriptor);
-            } else {
-              double_counters_.emplace(descriptor.index, descriptor);
-            }
-          } else {
-            EXPECT_EQ(descriptor.instrument_type,
-                      GlobalInstrumentsRegistry::InstrumentType::kHistogram);
-            if (descriptor.value_type ==
-                GlobalInstrumentsRegistry::ValueType::kUInt64) {
-              uint64_histograms_.emplace(descriptor.index, descriptor);
-            } else {
-              double_histograms_.emplace(descriptor.index, descriptor);
-            }
-          }
-        });
-  }
-
-  template <class T>
-  class Counter {
-   public:
-    explicit Counter(GlobalInstrumentsRegistry::GlobalInstrumentDescriptor u)
-        : name_(u.name),
-          description_(u.description),
-          unit_(u.unit),
-          label_keys_(std::move(u.label_keys)),
-          optional_label_keys_(std::move(u.optional_label_keys)) {}
-
-    void Add(T t, absl::Span<const absl::string_view> label_values,
-             absl::Span<const absl::string_view> optional_values) {
-      auto iter = storage_.find(MakeLabelString(
-          label_keys_, label_values, optional_label_keys_, optional_values));
-      if (iter != storage_.end()) {
-        iter->second += t;
-      } else {
-        storage_[MakeLabelString(label_keys_, label_values,
-                                 optional_label_keys_, optional_values)] = t;
-      }
-    }
-
-    absl::optional<T> GetValue(
-        absl::Span<const absl::string_view> label_values,
-        absl::Span<const absl::string_view> optional_values) {
-      auto iter = storage_.find(MakeLabelString(
-          label_keys_, label_values, optional_label_keys_, optional_values));
-      if (iter == storage_.end()) {
-        return absl::nullopt;
-      }
-      return iter->second;
-    }
-
-   private:
-    absl::string_view name_;
-    absl::string_view description_;
-    absl::string_view unit_;
-    std::vector<absl::string_view> label_keys_;
-    std::vector<absl::string_view> optional_label_keys_;
-    // Aggregation of the same key attributes.
-    absl::flat_hash_map<std::string, T> storage_;
-  };
-
-  template <class T>
-  class Histogram {
-   public:
-    explicit Histogram(GlobalInstrumentsRegistry::GlobalInstrumentDescriptor u)
-        : name_(u.name),
-          description_(u.description),
-          unit_(u.unit),
-          label_keys_(std::move(u.label_keys)),
-          optional_label_keys_(std::move(u.optional_label_keys)) {}
-
-    void Record(T t, absl::Span<const absl::string_view> label_values,
-                absl::Span<const absl::string_view> optional_values) {
-      std::string key = MakeLabelString(label_keys_, label_values,
-                                        optional_label_keys_, optional_values);
-      auto iter = storage_.find(key);
-      if (iter == storage_.end()) {
-        storage_.emplace(key, std::initializer_list<T>{t});
-      } else {
-        iter->second.push_back(t);
-      }
-    }
-
-    absl::optional<std::vector<T>> GetValues(
-        absl::Span<const absl::string_view> label_values,
-        absl::Span<const absl::string_view> optional_values) {
-      auto iter = storage_.find(MakeLabelString(
-          label_keys_, label_values, optional_label_keys_, optional_values));
-      if (iter == storage_.end()) {
-        return absl::nullopt;
-      }
-      return iter->second;
-    }
-
-   private:
-    absl::string_view name_;
-    absl::string_view description_;
-    absl::string_view unit_;
-    std::vector<absl::string_view> label_keys_;
-    std::vector<absl::string_view> optional_label_keys_;
-    absl::flat_hash_map<std::string, std::vector<T>> storage_;
-  };
-
-  absl::AnyInvocable<bool(const StatsPlugin::ChannelScope& /*scope*/) const>
-      channel_filter_;
-  // Instruments.
-  absl::flat_hash_map<uint32_t, Counter<uint64_t>> uint64_counters_;
-  absl::flat_hash_map<uint32_t, Counter<double>> double_counters_;
-  absl::flat_hash_map<uint32_t, Histogram<uint64_t>> uint64_histograms_;
-  absl::flat_hash_map<uint32_t, Histogram<double>> double_histograms_;
-};
-
-// TODO(yijiem): Move this to test/core/util/fake_stats_plugin.h
-class FakeStatsPluginBuilder {
- public:
-  FakeStatsPluginBuilder& SetChannelFilter(
-      absl::AnyInvocable<bool(const StatsPlugin::ChannelScope& /*scope*/) const>
-          channel_filter) {
-    channel_filter_ = std::move(channel_filter);
-    return *this;
-  }
-
-  std::shared_ptr<FakeStatsPlugin> BuildAndRegister() {
-    auto f = std::shared_ptr<FakeStatsPlugin>(
-        new FakeStatsPlugin(std::move(channel_filter_)));
-    GlobalStatsPluginRegistry::RegisterStatsPlugin(f);
-    return f;
-  }
-
- private:
-  absl::AnyInvocable<bool(const StatsPlugin::ChannelScope& /*scope*/) const>
-      channel_filter_;
-};
-
-std::shared_ptr<FakeStatsPlugin> MakeStatsPluginForTarget(
-    absl::string_view target_suffix) {
-  return FakeStatsPluginBuilder()
-      .SetChannelFilter(
-          [target_suffix](const StatsPlugin::ChannelScope& scope) {
-            return absl::EndsWith(scope.target(), target_suffix);
-          })
-      .BuildAndRegister();
-}
-
-class MetricsTest : public testing::Test {
+class MetricsTest : public ::testing::Test {
 public:
  void TearDown() override {
-    GlobalInstrumentsRegistry::TestOnlyResetGlobalInstrumentsRegistry();
-    GlobalStatsPluginRegistry::TestOnlyResetGlobalStatsPluginRegistry();
+    GlobalInstrumentsRegistryTestPeer::ResetGlobalInstrumentsRegistry();
+    GlobalStatsPluginRegistryTestPeer::ResetGlobalStatsPluginRegistry();
  }
 };

--- a/test/core/client_channel/lb_policy/BUILD
+++ b/test/core/client_channel/lb_policy/BUILD
@ -219,6 +219,7 @@ grpc_cc_test(
    uses_polling = False,
    deps = [
        "//:grpc",
+        "//test/core/util:fake_stats_plugin",
        "//test/core/util:grpc_test_util",
    ],
 )
@ -235,6 +236,7 @@ grpc_cc_test(
    deps = [
        ":lb_policy_test_lib",
        "//src/core:grpc_lb_policy_weighted_round_robin",
+        "//test/core/util:fake_stats_plugin",
        "//test/core/util:grpc_test_util",
    ],
 )
--- a/test/core/client_channel/lb_policy/lb_policy_test_lib.h
+++ b/test/core/client_channel/lb_policy/lb_policy_test_lib.h
@ -587,7 +587,9 @@ class LoadBalancingPolicyTest : public ::testing::Test {
      queue_.push_back(ReresolutionRequested());
    }

-    absl::string_view GetAuthority() override { return "server.example.com"; }
+    absl::string_view GetTarget() override { return test_->target_; }
+
+    absl::string_view GetAuthority() override { return test_->authority_; }

    RefCountedPtr<grpc_channel_credentials> GetChannelCredentials() override {
      return nullptr;
@ -602,6 +604,11 @@ class LoadBalancingPolicyTest : public ::testing::Test {
      return test_->fuzzing_ee_.get();
    }

+    GlobalStatsPluginRegistry::StatsPluginGroup& GetStatsPluginGroup()
+        override {
+      return test_->stats_plugin_group_;
+    }
+
    void AddTraceEvent(TraceSeverity, absl::string_view) override {}

    LoadBalancingPolicyTest* test_;
@ -1494,6 +1501,9 @@ class LoadBalancingPolicyTest : public ::testing::Test {
  OrphanablePtr<LoadBalancingPolicy> lb_policy_;
  const absl::string_view lb_policy_name_;
  const ChannelArgs channel_args_;
+  GlobalStatsPluginRegistry::StatsPluginGroup stats_plugin_group_;
+  std::string target_ = "dns:server.example.com";
+  std::string authority_ = "server.example.com";
 };

 }  // namespace testing
--- a/test/core/client_channel/lb_policy/weighted_round_robin_test.cc
+++ b/test/core/client_channel/lb_policy/weighted_round_robin_test.cc
@ -49,14 +49,18 @@
 #include "src/core/lib/json/json_writer.h"
 #include "src/core/load_balancing/backend_metric_data.h"
 #include "src/core/load_balancing/lb_policy.h"
+#include "src/core/load_balancing/weighted_target/weighted_target.h"
 #include "src/core/resolver/endpoint_addresses.h"
 #include "test/core/client_channel/lb_policy/lb_policy_test_lib.h"
+#include "test/core/util/fake_stats_plugin.h"
 #include "test/core/util/test_config.h"

 namespace grpc_core {
 namespace testing {
 namespace {

+constexpr absl::string_view kLocalityName = "locality0";
+
 class WeightedRoundRobinTest : public LoadBalancingPolicyTest {
 protected:
  class ConfigBuilder {
@ -103,7 +107,11 @@ class WeightedRoundRobinTest : public LoadBalancingPolicyTest {
    Json::Object json_;
  };

-  WeightedRoundRobinTest() : LoadBalancingPolicyTest("weighted_round_robin") {}
+  WeightedRoundRobinTest()
+      : LoadBalancingPolicyTest(
+            "weighted_round_robin",
+            ChannelArgs().Set(GRPC_ARG_LB_WEIGHTED_TARGET_CHILD,
+                              kLocalityName)) {}

  void SetUp() override {
    LoadBalancingPolicyTest::SetUp();
@ -989,6 +997,173 @@ TEST_F(WeightedRoundRobinTest, MultipleAddressesPerEndpoint) {
  EXPECT_FALSE(subchannel3_1->ConnectionRequested());
 }

+TEST_F(WeightedRoundRobinTest, MetricDefinitionRrFallback) {
+  const auto* descriptor =
+      GlobalInstrumentsRegistryTestPeer::FindMetricDescriptorByName(
+          "grpc.lb.wrr.rr_fallback");
+  ASSERT_NE(descriptor, nullptr);
+  EXPECT_EQ(descriptor->value_type,
+            GlobalInstrumentsRegistry::ValueType::kUInt64);
+  EXPECT_EQ(descriptor->instrument_type,
+            GlobalInstrumentsRegistry::InstrumentType::kCounter);
+  EXPECT_EQ(descriptor->enable_by_default, false);
+  EXPECT_EQ(descriptor->name, "grpc.lb.wrr.rr_fallback");
+  EXPECT_EQ(descriptor->unit, "{update}");
+  EXPECT_THAT(descriptor->label_keys, ::testing::ElementsAre("grpc.target"));
+  EXPECT_THAT(descriptor->optional_label_keys,
+              ::testing::ElementsAre("grpc.lb.locality"));
+}
+
+TEST_F(WeightedRoundRobinTest, MetricDefinitionEndpointWeightNotYetUsable) {
+  const auto* descriptor =
+      GlobalInstrumentsRegistryTestPeer::FindMetricDescriptorByName(
+          "grpc.lb.wrr.endpoint_weight_not_yet_usable");
+  ASSERT_NE(descriptor, nullptr);
+  EXPECT_EQ(descriptor->value_type,
+            GlobalInstrumentsRegistry::ValueType::kUInt64);
+  EXPECT_EQ(descriptor->instrument_type,
+            GlobalInstrumentsRegistry::InstrumentType::kCounter);
+  EXPECT_EQ(descriptor->enable_by_default, false);
+  EXPECT_EQ(descriptor->name, "grpc.lb.wrr.endpoint_weight_not_yet_usable");
+  EXPECT_EQ(descriptor->unit, "{endpoint}");
+  EXPECT_THAT(descriptor->label_keys, ::testing::ElementsAre("grpc.target"));
+  EXPECT_THAT(descriptor->optional_label_keys,
+              ::testing::ElementsAre("grpc.lb.locality"));
+}
+
+TEST_F(WeightedRoundRobinTest, MetricDefinitionEndpointWeightStale) {
+  const auto* descriptor =
+      GlobalInstrumentsRegistryTestPeer::FindMetricDescriptorByName(
+          "grpc.lb.wrr.endpoint_weight_stale");
+  ASSERT_NE(descriptor, nullptr);
+  EXPECT_EQ(descriptor->value_type,
+            GlobalInstrumentsRegistry::ValueType::kUInt64);
+  EXPECT_EQ(descriptor->instrument_type,
+            GlobalInstrumentsRegistry::InstrumentType::kCounter);
+  EXPECT_EQ(descriptor->enable_by_default, false);
+  EXPECT_EQ(descriptor->name, "grpc.lb.wrr.endpoint_weight_stale");
+  EXPECT_EQ(descriptor->unit, "{endpoint}");
+  EXPECT_THAT(descriptor->label_keys, ::testing::ElementsAre("grpc.target"));
+  EXPECT_THAT(descriptor->optional_label_keys,
+              ::testing::ElementsAre("grpc.lb.locality"));
+}
+
+TEST_F(WeightedRoundRobinTest, MetricDefinitionEndpointWeights) {
+  const auto* descriptor =
+      GlobalInstrumentsRegistryTestPeer::FindMetricDescriptorByName(
+          "grpc.lb.wrr.endpoint_weights");
+  ASSERT_NE(descriptor, nullptr);
+  EXPECT_EQ(descriptor->value_type,
+            GlobalInstrumentsRegistry::ValueType::kDouble);
+  EXPECT_EQ(descriptor->instrument_type,
+            GlobalInstrumentsRegistry::InstrumentType::kHistogram);
+  EXPECT_EQ(descriptor->enable_by_default, false);
+  EXPECT_EQ(descriptor->name, "grpc.lb.wrr.endpoint_weights");
+  EXPECT_EQ(descriptor->unit, "{weight}");
+  EXPECT_THAT(descriptor->label_keys, ::testing::ElementsAre("grpc.target"));
+  EXPECT_THAT(descriptor->optional_label_keys,
+              ::testing::ElementsAre("grpc.lb.locality"));
+}
+
+TEST_F(WeightedRoundRobinTest, MetricValues) {
+  if (!IsWrrDelegateToPickFirstEnabled()) return;
+  const auto kRrFallback =
+      GlobalInstrumentsRegistryTestPeer::FindUInt64CounterHandleByName(
+          "grpc.lb.wrr.rr_fallback")
+          .value();
+  const auto kEndpointWeightNotYetUsable =
+      GlobalInstrumentsRegistryTestPeer::FindUInt64CounterHandleByName(
+          "grpc.lb.wrr.endpoint_weight_not_yet_usable")
+          .value();
+  const auto kEndpointWeightStale =
+      GlobalInstrumentsRegistryTestPeer::FindUInt64CounterHandleByName(
+          "grpc.lb.wrr.endpoint_weight_stale")
+          .value();
+  const auto kEndpointWeights =
+      GlobalInstrumentsRegistryTestPeer::FindDoubleHistogramHandleByName(
+          "grpc.lb.wrr.endpoint_weights")
+          .value();
+  const absl::string_view kLabelValues[] = {target_};
+  const absl::string_view kOptionalLabelValues[] = {kLocalityName};
+  auto stats_plugin = std::make_shared<FakeStatsPlugin>(
+      nullptr, /*use_disabled_by_default_metrics=*/true);
+  stats_plugin_group_.push_back(stats_plugin);
+  // Send address list to LB policy.
+  const std::array<absl::string_view, 3> kAddresses = {
+      "ipv4:127.0.0.1:441", "ipv4:127.0.0.1:442", "ipv4:127.0.0.1:443"};
+  auto picker = SendInitialUpdateAndWaitForConnected(
+      kAddresses,
+      ConfigBuilder().SetWeightExpirationPeriod(Duration::Seconds(2)));
+  ASSERT_NE(picker, nullptr);
+  // Address 0 gets weight 1, address 1 gets weight 3.
+  // No utilization report from backend 2, so it gets the average weight 2.
+  WaitForWeightedRoundRobinPicks(
+      &picker,
+      {{kAddresses[0], MakeBackendMetricData(/*app_utilization=*/0.9,
+                                             /*qps=*/100.0, /*eps=*/0.0)},
+       {kAddresses[1], MakeBackendMetricData(/*app_utilization=*/0.3,
+                                             /*qps=*/100.0, /*eps=*/0.0)}},
+      {{kAddresses[0], 1}, {kAddresses[1], 3}, {kAddresses[2], 2}});
+  // Now have backend 2 report utilization the same as backend 1, so its
+  // weight will be the same.
+  WaitForWeightedRoundRobinPicks(
+      &picker,
+      {{kAddresses[0], MakeBackendMetricData(/*app_utilization=*/0.9,
+                                             /*qps=*/100.0, /*eps=*/0.0)},
+       {kAddresses[1], MakeBackendMetricData(/*app_utilization=*/0.3,
+                                             /*qps=*/100.0, /*eps=*/0.0)},
+       {kAddresses[2], MakeBackendMetricData(/*app_utilization=*/0.3,
+                                             /*qps=*/100.0, /*eps=*/0.0)}},
+      {{kAddresses[0], 1}, {kAddresses[1], 3}, {kAddresses[2], 3}});
+  // Check endpoint weights.
+  EXPECT_THAT(stats_plugin->GetHistogramValue(kEndpointWeights, kLabelValues,
+                                              kOptionalLabelValues),
+              ::testing::Optional(::testing::ElementsAre(
+                  // Picker created for first endpoint becoming READY.
+                  0,
+                  // Picker update for second endpoint CONNECTING.
+                  0,
+                  // Picker update for second endpoint READY.
+                  0, 0,
+                  // Picker update for third endpoint CONNECTING.
+                  0, 0,
+                  // Picker update for third endpoint READY.
+                  0, 0, 0,
+                  // Weights for first two endpoints now start getting used.
+                  ::testing::DoubleNear(111.111115, 0.000001),
+                  ::testing::DoubleNear(333.333344, 0.000001), 0,
+                  // Weights for all endpoints are now used.
+                  ::testing::DoubleNear(111.111115, 0.000001),
+                  ::testing::DoubleNear(333.333344, 0.000001),
+                  ::testing::DoubleNear(333.333344, 0.000001))));
+  // RR fallback should trigger for the first 5 updates above, because
+  // there are less than two endpoints with valid weights.
+  EXPECT_THAT(stats_plugin->GetCounterValue(kRrFallback, kLabelValues,
+                                            kOptionalLabelValues),
+              ::testing::Optional(5));
+  // Endpoint-not-yet-usable will be incremented once for every endpoint
+  // with weight 0 above.
+  EXPECT_THAT(stats_plugin->GetCounterValue(kEndpointWeightNotYetUsable,
+                                            kLabelValues, kOptionalLabelValues),
+              ::testing::Optional(10));
+  // There are no stale endpoint weights so far.
+  EXPECT_THAT(stats_plugin->GetCounterValue(kEndpointWeightStale, kLabelValues,
+                                            kOptionalLabelValues),
+              ::testing::Optional(0));
+  // Advance time to make weights stale and trigger the timer callback
+  // to recompute weights.
+  gpr_log(GPR_INFO, "advancing time to trigger staleness...");
+  IncrementTimeBy(Duration::Seconds(2));
+  // Picker should now be falling back to round-robin.
+  ExpectWeightedRoundRobinPicks(
+      picker.get(), {},
+      {{kAddresses[0], 3}, {kAddresses[1], 3}, {kAddresses[2], 3}});
+  // All three endpoints should now have stale weights.
+  EXPECT_THAT(stats_plugin->GetCounterValue(kEndpointWeightStale, kLabelValues,
+                                            kOptionalLabelValues),
+              ::testing::Optional(3));
+}
+
 }  // namespace
 }  // namespace testing
 }  // namespace grpc_core
--- a/test/core/util/BUILD
+++ b/test/core/util/BUILD
@ -494,10 +494,21 @@ grpc_cc_library(

 grpc_cc_library(
    name = "fake_stats_plugin",
+    testonly = True,
    srcs = ["fake_stats_plugin.cc"],
    hdrs = ["fake_stats_plugin.h"],
+    external_deps = [
+        "absl/container:flat_hash_map",
+        "absl/functional:any_invocable",
+        "absl/status",
+        "absl/strings",
+        "absl/types:optional",
+        "absl/types:span",
+        "gtest",
+    ],
    deps = [
        "//:grpc",
        "//src/core:examine_stack",
+        "//src/core:metrics",
    ],
 )
--- a/test/core/util/fake_stats_plugin.cc
+++ b/test/core/util/fake_stats_plugin.cc
@ -79,4 +79,109 @@ void RegisterFakeStatsPlugin() {
      });
 }

+namespace {
+
+void AddKeyValuePairs(absl::Span<const absl::string_view> keys,
+                      absl::Span<const absl::string_view> values,
+                      std::vector<std::string>* key_value_pairs) {
+  GPR_ASSERT(keys.size() == values.size());
+  for (size_t i = 0; i < keys.size(); ++i) {
+    key_value_pairs->push_back(absl::StrCat(keys[i], "=", values[i]));
+  }
+}
+
+}  // namespace
+
+std::string MakeLabelString(
+    absl::Span<const absl::string_view> label_keys,
+    absl::Span<const absl::string_view> label_values,
+    absl::Span<const absl::string_view> optional_label_keys,
+    absl::Span<const absl::string_view> optional_values) {
+  std::vector<std::string> key_value_pairs;
+  AddKeyValuePairs(label_keys, label_values, &key_value_pairs);
+  AddKeyValuePairs(optional_label_keys, optional_values, &key_value_pairs);
+  return absl::StrJoin(key_value_pairs, ",");
+}
+
+std::shared_ptr<FakeStatsPlugin> MakeStatsPluginForTarget(
+    absl::string_view target_suffix) {
+  return FakeStatsPluginBuilder()
+      .SetChannelFilter(
+          [target_suffix](const StatsPlugin::ChannelScope& scope) {
+            return absl::EndsWith(scope.target(), target_suffix);
+          })
+      .BuildAndRegister();
+}
+
+void GlobalInstrumentsRegistryTestPeer::ResetGlobalInstrumentsRegistry() {
+  auto& instruments = GlobalInstrumentsRegistry::GetInstrumentList();
+  instruments.clear();
+}
+
+namespace {
+
+template <typename HandleType>
+absl::optional<HandleType> FindInstrument(
+    const absl::flat_hash_map<
+        absl::string_view,
+        GlobalInstrumentsRegistry::GlobalInstrumentDescriptor>& instruments,
+    absl::string_view name, GlobalInstrumentsRegistry::ValueType value_type,
+    GlobalInstrumentsRegistry::InstrumentType instrument_type) {
+  auto it = instruments.find(name);
+  if (it != instruments.end() && it->second.value_type == value_type &&
+      it->second.instrument_type == instrument_type) {
+    HandleType handle;
+    handle.index = it->second.index;
+    return handle;
+  }
+  return absl::nullopt;
+}
+
+}  // namespace
+
+absl::optional<GlobalInstrumentsRegistry::GlobalUInt64CounterHandle>
+GlobalInstrumentsRegistryTestPeer::FindUInt64CounterHandleByName(
+    absl::string_view name) {
+  return FindInstrument<GlobalInstrumentsRegistry::GlobalUInt64CounterHandle>(
+      GlobalInstrumentsRegistry::GetInstrumentList(), name,
+      GlobalInstrumentsRegistry::ValueType::kUInt64,
+      GlobalInstrumentsRegistry::InstrumentType::kCounter);
+}
+
+absl::optional<GlobalInstrumentsRegistry::GlobalDoubleCounterHandle>
+GlobalInstrumentsRegistryTestPeer::FindDoubleCounterHandleByName(
+    absl::string_view name) {
+  return FindInstrument<GlobalInstrumentsRegistry::GlobalDoubleCounterHandle>(
+      GlobalInstrumentsRegistry::GetInstrumentList(), name,
+      GlobalInstrumentsRegistry::ValueType::kDouble,
+      GlobalInstrumentsRegistry::InstrumentType::kCounter);
+}
+
+absl::optional<GlobalInstrumentsRegistry::GlobalUInt64HistogramHandle>
+GlobalInstrumentsRegistryTestPeer::FindUInt64HistogramHandleByName(
+    absl::string_view name) {
+  return FindInstrument<GlobalInstrumentsRegistry::GlobalUInt64HistogramHandle>(
+      GlobalInstrumentsRegistry::GetInstrumentList(), name,
+      GlobalInstrumentsRegistry::ValueType::kUInt64,
+      GlobalInstrumentsRegistry::InstrumentType::kHistogram);
+}
+
+absl::optional<GlobalInstrumentsRegistry::GlobalDoubleHistogramHandle>
+GlobalInstrumentsRegistryTestPeer::FindDoubleHistogramHandleByName(
+    absl::string_view name) {
+  return FindInstrument<GlobalInstrumentsRegistry::GlobalDoubleHistogramHandle>(
+      GlobalInstrumentsRegistry::GetInstrumentList(), name,
+      GlobalInstrumentsRegistry::ValueType::kDouble,
+      GlobalInstrumentsRegistry::InstrumentType::kHistogram);
+}
+
+GlobalInstrumentsRegistry::GlobalInstrumentDescriptor*
+GlobalInstrumentsRegistryTestPeer::FindMetricDescriptorByName(
+    absl::string_view name) {
+  auto& instruments = GlobalInstrumentsRegistry::GetInstrumentList();
+  auto it = instruments.find(name);
+  if (it != instruments.end()) return &it->second;
+  return nullptr;
+}
+
 }  // namespace grpc_core
--- a/test/core/util/fake_stats_plugin.h
+++ b/test/core/util/fake_stats_plugin.h
@ -19,7 +19,16 @@
 #include <string>
 #include <vector>

+#include "absl/container/flat_hash_map.h"
+#include "absl/functional/any_invocable.h"
+#include "absl/status/status.h"
+#include "absl/strings/string_view.h"
+#include "absl/types/optional.h"
+#include "absl/types/span.h"
+#include "gmock/gmock.h"
+
 #include "src/core/lib/channel/call_tracer.h"
+#include "src/core/lib/channel/metrics.h"
 #include "src/core/lib/channel/promise_based_filter.h"
 #include "src/core/lib/channel/tcp_tracer.h"

@ -187,6 +196,315 @@ class FakeServerCallTracer : public ServerCallTracer {
  std::vector<std::string>* annotation_logger_;
 };

+std::string MakeLabelString(
+    absl::Span<const absl::string_view> label_keys,
+    absl::Span<const absl::string_view> label_values,
+    absl::Span<const absl::string_view> optional_label_keys,
+    absl::Span<const absl::string_view> optional_values);
+
+class FakeStatsPlugin : public StatsPlugin {
+ public:
+  explicit FakeStatsPlugin(
+      absl::AnyInvocable<bool(const ChannelScope& /*scope*/) const>
+          channel_filter = nullptr,
+      bool use_disabled_by_default_metrics = false)
+      : channel_filter_(std::move(channel_filter)) {
+    GlobalInstrumentsRegistry::ForEach(
+        [&](const GlobalInstrumentsRegistry::GlobalInstrumentDescriptor&
+                descriptor) {
+          if (!use_disabled_by_default_metrics &&
+              !descriptor.enable_by_default) {
+            gpr_log(GPR_INFO,
+                    "FakeStatsPlugin[%p]: skipping disabled metric: %s", this,
+                    std::string(descriptor.name).c_str());
+            return;
+          }
+          if (descriptor.instrument_type ==
+              GlobalInstrumentsRegistry::InstrumentType::kCounter) {
+            if (descriptor.value_type ==
+                GlobalInstrumentsRegistry::ValueType::kUInt64) {
+              uint64_counters_.emplace(descriptor.index, descriptor);
+            } else {
+              double_counters_.emplace(descriptor.index, descriptor);
+            }
+          } else {
+            EXPECT_EQ(descriptor.instrument_type,
+                      GlobalInstrumentsRegistry::InstrumentType::kHistogram);
+            if (descriptor.value_type ==
+                GlobalInstrumentsRegistry::ValueType::kUInt64) {
+              uint64_histograms_.emplace(descriptor.index, descriptor);
+            } else {
+              double_histograms_.emplace(descriptor.index, descriptor);
+            }
+          }
+        });
+  }
+
+  bool IsEnabledForChannel(const ChannelScope& scope) const override {
+    if (channel_filter_ == nullptr) return true;
+    return channel_filter_(scope);
+  }
+
+  bool IsEnabledForServer(const ChannelArgs& /*args*/) const override {
+    return false;
+  }
+
+  void AddCounter(
+      GlobalInstrumentsRegistry::GlobalUInt64CounterHandle handle,
+      uint64_t value, absl::Span<const absl::string_view> label_values,
+      absl::Span<const absl::string_view> optional_values) override {
+    // The problem with this approach is that we initialize uint64_counters_ in
+    // BuildAndRegister by querying the GlobalInstrumentsRegistry at the time.
+    // If the GlobalInstrumentsRegistry has changed since then (which we
+    // currently don't allow), we might not have seen that descriptor nor have
+    // we created an instrument for it. We probably could copy the existing
+    // instruments at build time and for the handle that we haven't seen we will
+    // just ignore it here. This would also prevent us from having to lock the
+    // GlobalInstrumentsRegistry everytime a metric is recorded. But this is not
+    // a concern for now.
+    gpr_log(GPR_INFO,
+            "FakeStatsPlugin[%p]::AddCounter(index=%u, value=(uint64)%lu, "
+            "label_values={%s}, optional_label_values={%s}",
+            this, handle.index, value,
+            absl::StrJoin(label_values, ", ").c_str(),
+            absl::StrJoin(optional_values, ", ").c_str());
+    auto iter = uint64_counters_.find(handle.index);
+    if (iter == uint64_counters_.end()) return;
+    iter->second.Add(value, label_values, optional_values);
+  }
+  void AddCounter(
+      GlobalInstrumentsRegistry::GlobalDoubleCounterHandle handle, double value,
+      absl::Span<const absl::string_view> label_values,
+      absl::Span<const absl::string_view> optional_values) override {
+    gpr_log(GPR_INFO,
+            "FakeStatsPlugin[%p]::AddCounter(index=%u, value(double)=%f, "
+            "label_values={%s}, optional_label_values={%s}",
+            this, handle.index, value,
+            absl::StrJoin(label_values, ", ").c_str(),
+            absl::StrJoin(optional_values, ", ").c_str());
+    auto iter = double_counters_.find(handle.index);
+    if (iter == double_counters_.end()) return;
+    iter->second.Add(value, label_values, optional_values);
+  }
+  void RecordHistogram(
+      GlobalInstrumentsRegistry::GlobalUInt64HistogramHandle handle,
+      uint64_t value, absl::Span<const absl::string_view> label_values,
+      absl::Span<const absl::string_view> optional_values) override {
+    gpr_log(GPR_INFO,
+            "FakeStatsPlugin[%p]::RecordHistogram(index=%u, value=(uint64)%lu, "
+            "label_values={%s}, optional_label_values={%s}",
+            this, handle.index, value,
+            absl::StrJoin(label_values, ", ").c_str(),
+            absl::StrJoin(optional_values, ", ").c_str());
+    auto iter = uint64_histograms_.find(handle.index);
+    if (iter == uint64_histograms_.end()) return;
+    iter->second.Record(value, label_values, optional_values);
+  }
+  void RecordHistogram(
+      GlobalInstrumentsRegistry::GlobalDoubleHistogramHandle handle,
+      double value, absl::Span<const absl::string_view> label_values,
+      absl::Span<const absl::string_view> optional_values) override {
+    gpr_log(GPR_INFO,
+            "FakeStatsPlugin[%p]::RecordHistogram(index=%u, value=(double)%f, "
+            "label_values={%s}, optional_label_values={%s}",
+            this, handle.index, value,
+            absl::StrJoin(label_values, ", ").c_str(),
+            absl::StrJoin(optional_values, ", ").c_str());
+    auto iter = double_histograms_.find(handle.index);
+    if (iter == double_histograms_.end()) return;
+    iter->second.Record(value, label_values, optional_values);
+  }
+
+  absl::optional<uint64_t> GetCounterValue(
+      GlobalInstrumentsRegistry::GlobalUInt64CounterHandle handle,
+      absl::Span<const absl::string_view> label_values,
+      absl::Span<const absl::string_view> optional_values) {
+    auto iter = uint64_counters_.find(handle.index);
+    if (iter == uint64_counters_.end()) {
+      return absl::nullopt;
+    }
+    return iter->second.GetValue(label_values, optional_values);
+  }
+  absl::optional<double> GetCounterValue(
+      GlobalInstrumentsRegistry::GlobalDoubleCounterHandle handle,
+      absl::Span<const absl::string_view> label_values,
+      absl::Span<const absl::string_view> optional_values) {
+    auto iter = double_counters_.find(handle.index);
+    if (iter == double_counters_.end()) {
+      return absl::nullopt;
+    }
+    return iter->second.GetValue(label_values, optional_values);
+  }
+  absl::optional<std::vector<uint64_t>> GetHistogramValue(
+      GlobalInstrumentsRegistry::GlobalUInt64HistogramHandle handle,
+      absl::Span<const absl::string_view> label_values,
+      absl::Span<const absl::string_view> optional_values) {
+    auto iter = uint64_histograms_.find(handle.index);
+    if (iter == uint64_histograms_.end()) {
+      return absl::nullopt;
+    }
+    return iter->second.GetValues(label_values, optional_values);
+  }
+  absl::optional<std::vector<double>> GetHistogramValue(
+      GlobalInstrumentsRegistry::GlobalDoubleHistogramHandle handle,
+      absl::Span<const absl::string_view> label_values,
+      absl::Span<const absl::string_view> optional_values) {
+    auto iter = double_histograms_.find(handle.index);
+    if (iter == double_histograms_.end()) {
+      return absl::nullopt;
+    }
+    return iter->second.GetValues(label_values, optional_values);
+  }
+
+ private:
+  template <class T>
+  class Counter {
+   public:
+    explicit Counter(GlobalInstrumentsRegistry::GlobalInstrumentDescriptor u)
+        : name_(u.name),
+          description_(u.description),
+          unit_(u.unit),
+          label_keys_(std::move(u.label_keys)),
+          optional_label_keys_(std::move(u.optional_label_keys)) {}
+
+    void Add(T t, absl::Span<const absl::string_view> label_values,
+             absl::Span<const absl::string_view> optional_values) {
+      auto iter = storage_.find(MakeLabelString(
+          label_keys_, label_values, optional_label_keys_, optional_values));
+      if (iter != storage_.end()) {
+        iter->second += t;
+      } else {
+        storage_[MakeLabelString(label_keys_, label_values,
+                                 optional_label_keys_, optional_values)] = t;
+      }
+    }
+
+    absl::optional<T> GetValue(
+        absl::Span<const absl::string_view> label_values,
+        absl::Span<const absl::string_view> optional_values) {
+      auto iter = storage_.find(MakeLabelString(
+          label_keys_, label_values, optional_label_keys_, optional_values));
+      if (iter == storage_.end()) {
+        return absl::nullopt;
+      }
+      return iter->second;
+    }
+
+   private:
+    absl::string_view name_;
+    absl::string_view description_;
+    absl::string_view unit_;
+    std::vector<absl::string_view> label_keys_;
+    std::vector<absl::string_view> optional_label_keys_;
+    // Aggregation of the same key attributes.
+    absl::flat_hash_map<std::string, T> storage_;
+  };
+
+  template <class T>
+  class Histogram {
+   public:
+    explicit Histogram(GlobalInstrumentsRegistry::GlobalInstrumentDescriptor u)
+        : name_(u.name),
+          description_(u.description),
+          unit_(u.unit),
+          label_keys_(std::move(u.label_keys)),
+          optional_label_keys_(std::move(u.optional_label_keys)) {}
+
+    void Record(T t, absl::Span<const absl::string_view> label_values,
+                absl::Span<const absl::string_view> optional_values) {
+      std::string key = MakeLabelString(label_keys_, label_values,
+                                        optional_label_keys_, optional_values);
+      auto iter = storage_.find(key);
+      if (iter == storage_.end()) {
+        storage_.emplace(key, std::initializer_list<T>{t});
+      } else {
+        iter->second.push_back(t);
+      }
+    }
+
+    absl::optional<std::vector<T>> GetValues(
+        absl::Span<const absl::string_view> label_values,
+        absl::Span<const absl::string_view> optional_values) {
+      auto iter = storage_.find(MakeLabelString(
+          label_keys_, label_values, optional_label_keys_, optional_values));
+      if (iter == storage_.end()) {
+        return absl::nullopt;
+      }
+      return iter->second;
+    }
+
+   private:
+    absl::string_view name_;
+    absl::string_view description_;
+    absl::string_view unit_;
+    std::vector<absl::string_view> label_keys_;
+    std::vector<absl::string_view> optional_label_keys_;
+    absl::flat_hash_map<std::string, std::vector<T>> storage_;
+  };
+
+  absl::AnyInvocable<bool(const ChannelScope& /*scope*/) const> channel_filter_;
+  // Instruments.
+  absl::flat_hash_map<uint32_t, Counter<uint64_t>> uint64_counters_;
+  absl::flat_hash_map<uint32_t, Counter<double>> double_counters_;
+  absl::flat_hash_map<uint32_t, Histogram<uint64_t>> uint64_histograms_;
+  absl::flat_hash_map<uint32_t, Histogram<double>> double_histograms_;
+};
+
+class FakeStatsPluginBuilder {
+ public:
+  FakeStatsPluginBuilder& SetChannelFilter(
+      absl::AnyInvocable<bool(const StatsPlugin::ChannelScope& /*scope*/) const>
+          channel_filter) {
+    channel_filter_ = std::move(channel_filter);
+    return *this;
+  }
+
+  FakeStatsPluginBuilder& UseDisabledByDefaultMetrics(bool value) {
+    use_disabled_by_default_metrics_ = value;
+    return *this;
+  }
+
+  std::shared_ptr<FakeStatsPlugin> BuildAndRegister() {
+    auto f = std::make_shared<FakeStatsPlugin>(
+        std::move(channel_filter_), use_disabled_by_default_metrics_);
+    GlobalStatsPluginRegistry::RegisterStatsPlugin(f);
+    return f;
+  }
+
+ private:
+  absl::AnyInvocable<bool(const StatsPlugin::ChannelScope& /*scope*/) const>
+      channel_filter_;
+  bool use_disabled_by_default_metrics_ = false;
+};
+
+std::shared_ptr<FakeStatsPlugin> MakeStatsPluginForTarget(
+    absl::string_view target_suffix);
+
+class GlobalInstrumentsRegistryTestPeer {
+ public:
+  static void ResetGlobalInstrumentsRegistry();
+
+  static absl::optional<GlobalInstrumentsRegistry::GlobalUInt64CounterHandle>
+  FindUInt64CounterHandleByName(absl::string_view name);
+  static absl::optional<GlobalInstrumentsRegistry::GlobalDoubleCounterHandle>
+  FindDoubleCounterHandleByName(absl::string_view name);
+  static absl::optional<GlobalInstrumentsRegistry::GlobalUInt64HistogramHandle>
+  FindUInt64HistogramHandleByName(absl::string_view name);
+  static absl::optional<GlobalInstrumentsRegistry::GlobalDoubleHistogramHandle>
+  FindDoubleHistogramHandleByName(absl::string_view name);
+
+  static GlobalInstrumentsRegistry::GlobalInstrumentDescriptor*
+  FindMetricDescriptorByName(absl::string_view name);
+};
+
+class GlobalStatsPluginRegistryTestPeer {
+ public:
+  static void ResetGlobalStatsPluginRegistry() {
+    MutexLock lock(&*GlobalStatsPluginRegistry::mutex_);
+    GlobalStatsPluginRegistry::plugins_->clear();
+  }
+};
+
 }  // namespace grpc_core

 #endif  // GRPC_TEST_CORE_UTIL_FAKE_STATS_PLUGIN_H
--- a/test/cpp/end2end/xds/BUILD
+++ b/test/cpp/end2end/xds/BUILD
@ -329,6 +329,7 @@ grpc_cc_test(
        "//src/proto/grpc/testing/xds/v3:client_side_weighted_round_robin_proto",
        "//src/proto/grpc/testing/xds/v3:cluster_proto",
        "//src/proto/grpc/testing/xds/v3:wrr_locality_proto",
+        "//test/core/util:fake_stats_plugin",
        "//test/core/util:grpc_test_util",
        "//test/core/util:scoped_env_var",
    ],
--- a/test/cpp/end2end/xds/xds_wrr_end2end_test.cc
+++ b/test/cpp/end2end/xds/xds_wrr_end2end_test.cc
@ -27,8 +27,10 @@

 #include "src/core/client_channel/backup_poller.h"
 #include "src/core/lib/config/config_vars.h"
+#include "src/core/lib/experiments/experiments.h"
 #include "src/proto/grpc/testing/xds/v3/client_side_weighted_round_robin.grpc.pb.h"
 #include "src/proto/grpc/testing/xds/v3/wrr_locality.grpc.pb.h"
+#include "test/core/util/fake_stats_plugin.h"
 #include "test/core/util/scoped_env_var.h"
 #include "test/cpp/end2end/xds/xds_end2end_test_lib.h"

@ -40,12 +42,25 @@ using ::envoy::extensions::load_balancing_policies::
    client_side_weighted_round_robin::v3::ClientSideWeightedRoundRobin;
 using ::envoy::extensions::load_balancing_policies::wrr_locality::v3::
    WrrLocality;
-using WrrTest = XdsEnd2endTest;
+
+class WrrTest : public XdsEnd2endTest {
+ protected:
+  void SetUp() override {
+    // No-op -- tests must explicitly call InitClient().
+  }
+
+  static std::string LocalityNameString(absl::string_view sub_zone) {
+    return absl::StrFormat("{region=\"%s\", zone=\"%s\", sub_zone=\"%s\"}",
+                           kDefaultLocalityRegion, kDefaultLocalityZone,
+                           sub_zone);
+  }
+};

 INSTANTIATE_TEST_SUITE_P(XdsTest, WrrTest, ::testing::Values(XdsTestType()),
                         &XdsTestType::Name);

 TEST_P(WrrTest, Basic) {
+  InitClient();
  CreateAndStartBackends(3);
  // Expected weights = qps / (util + (eps/qps)) =
  //   1/(0.2+0.2) : 1/(0.3+0.3) : 2/(1.5+0.1) = 6:4:3
@ -92,6 +107,48 @@ TEST_P(WrrTest, Basic) {
  });
 }

+TEST_P(WrrTest, MetricsHaveLocalityLabel) {
+  if (!grpc_core::IsWrrDelegateToPickFirstEnabled()) return;
+  const auto kEndpointWeights =
+      grpc_core::GlobalInstrumentsRegistryTestPeer::
+          FindDoubleHistogramHandleByName("grpc.lb.wrr.endpoint_weights")
+              .value();
+  const std::string target = absl::StrCat("xds:", kServerName);
+  const absl::string_view kLabelValues[] = {/*target=*/target};
+  // Register stats plugin before initializing client.
+  auto stats_plugin = grpc_core::FakeStatsPluginBuilder()
+                          .UseDisabledByDefaultMetrics(true)
+                          .BuildAndRegister();
+  InitClient();
+  CreateAndStartBackends(2);
+  auto cluster = default_cluster_;
+  WrrLocality wrr_locality;
+  wrr_locality.mutable_endpoint_picking_policy()
+      ->add_policies()
+      ->mutable_typed_extension_config()
+      ->mutable_typed_config()
+      ->PackFrom(ClientSideWeightedRoundRobin());
+  cluster.mutable_load_balancing_policy()
+      ->add_policies()
+      ->mutable_typed_extension_config()
+      ->mutable_typed_config()
+      ->PackFrom(wrr_locality);
+  balancer_->ads_service()->SetCdsResource(cluster);
+  EdsResourceArgs args({{"locality0", CreateEndpointsForBackends(0, 1)},
+                        {"locality1", CreateEndpointsForBackends(1, 2)}});
+  balancer_->ads_service()->SetEdsResource(BuildEdsResource(args));
+  WaitForAllBackends(DEBUG_LOCATION);
+  // Make sure we have a metric value for each of the two localities.
+  EXPECT_THAT(
+      stats_plugin->GetHistogramValue(kEndpointWeights, kLabelValues,
+                                      {LocalityNameString("locality0")}),
+      ::testing::Optional(::testing::Not(::testing::IsEmpty())));
+  EXPECT_THAT(
+      stats_plugin->GetHistogramValue(kEndpointWeights, kLabelValues,
+                                      {LocalityNameString("locality1")}),
+      ::testing::Optional(::testing::Not(::testing::IsEmpty())));
+}
+
 }  // namespace
 }  // namespace testing
 }  // namespace grpc
--- a/tools/doxygen/Doxyfile.c++.internal
+++ b/tools/doxygen/Doxyfile.c++.internal
@ -2160,6 +2160,8 @@ src/core/lib/channel/channelz_registry.h \
 src/core/lib/channel/connected_channel.cc \
 src/core/lib/channel/connected_channel.h \
 src/core/lib/channel/context.h \
+src/core/lib/channel/metrics.cc \
+src/core/lib/channel/metrics.h \
 src/core/lib/channel/promise_based_filter.cc \
 src/core/lib/channel/promise_based_filter.h \
 src/core/lib/channel/server_call_tracer_filter.cc \
@ -2891,6 +2893,7 @@ src/core/load_balancing/weighted_round_robin/static_stride_scheduler.cc \
 src/core/load_balancing/weighted_round_robin/static_stride_scheduler.h \
 src/core/load_balancing/weighted_round_robin/weighted_round_robin.cc \
 src/core/load_balancing/weighted_target/weighted_target.cc \
+src/core/load_balancing/weighted_target/weighted_target.h \
 src/core/load_balancing/xds/cds.cc \
 src/core/load_balancing/xds/xds_channel_args.h \
 src/core/load_balancing/xds/xds_cluster_impl.cc \
--- a/tools/doxygen/Doxyfile.core.internal
+++ b/tools/doxygen/Doxyfile.core.internal
@ -1932,6 +1932,8 @@ src/core/lib/channel/channelz_registry.h \
 src/core/lib/channel/connected_channel.cc \
 src/core/lib/channel/connected_channel.h \
 src/core/lib/channel/context.h \
+src/core/lib/channel/metrics.cc \
+src/core/lib/channel/metrics.h \
 src/core/lib/channel/promise_based_filter.cc \
 src/core/lib/channel/promise_based_filter.h \
 src/core/lib/channel/server_call_tracer_filter.cc \
@ -2668,6 +2670,7 @@ src/core/load_balancing/weighted_round_robin/static_stride_scheduler.cc \
 src/core/load_balancing/weighted_round_robin/static_stride_scheduler.h \
 src/core/load_balancing/weighted_round_robin/weighted_round_robin.cc \
 src/core/load_balancing/weighted_target/weighted_target.cc \
+src/core/load_balancing/weighted_target/weighted_target.h \
 src/core/load_balancing/xds/cds.cc \
 src/core/load_balancing/xds/xds_channel_args.h \
 src/core/load_balancing/xds/xds_cluster_impl.cc \