[metrics][EPLB]: Support selected count of physical experts on each GPU (#9825)

docs/references/environment_variables.md

@@ -7,13 +7,14 @@ SGLang supports various environment variables that can be used to configure its
 ## General Configuration
 
 | Environment Variable                      | Description                                                                                                                      | Default Value |
-| --- | --- | --- |
+|-------------------------------------------|----------------------------------------------------------------------------------------------------------------------------------|---------------|
 | `SGLANG_USE_MODELSCOPE`                   | Enable using models from ModelScope                                                                                              | `false`       |
 | `SGLANG_HOST_IP`                          | Host IP address for the server                                                                                                   | `0.0.0.0`     |
 | `SGLANG_PORT`                             | Port for the server                                                                                                              | auto-detected |
 | `SGLANG_LOGGING_CONFIG_PATH`              | Custom logging configuration path                                                                                                | Not set       |
 | `SGLANG_DISABLE_REQUEST_LOGGING`          | Disable request logging                                                                                                          | `false`       |
 | `SGLANG_HEALTH_CHECK_TIMEOUT`             | Timeout for health check in seconds                                                                                              | `20`          |
+| `SGLANG_EPLB_HEATMAP_COLLECTION_INTERVAL` | The interval of passes to collect the metric of selected count of physical experts on each layer and GPU rank. 0 means disabled. | `0`           |
 
 ## Performance Tuning
 

python/sglang/srt/eplb/expert_distribution.py

@@ -28,6 +28,7 @@ import torch
 import torch.distributed
 
 from sglang.srt.environ import envs
+from sglang.srt.metrics.collector import ExpertDispatchCollector
 from sglang.srt.model_executor.forward_batch_info import ForwardBatch
 from sglang.srt.server_args import ServerArgs
 from sglang.srt.utils import Withable, is_npu
@@ -661,6 +662,10 @@ class _UtilizationRateAccumulatorMixin(_Accumulator):
             self.window_sizes = [10, 100, 1000]
             self._history = _DequeCollection(maxlens=self.window_sizes)
             self._rank = torch.distributed.get_rank()
+            self._expert_dispatch_collector = ExpertDispatchCollector(
+                self._expert_location_metadata.ep_size
+            )
+            self._collection_counter = 0
 
     def append(
         self,
@@ -692,6 +697,8 @@ class _UtilizationRateAccumulatorMixin(_Accumulator):
         )
 
         if self._rank == 0:
+            self._collect_metrics_if_needed(gpu_physical_count)
+
             utilization_rate_tensor = compute_utilization_rate(gpu_physical_count)
             utilization_rate = torch.mean(utilization_rate_tensor).item()
             self._history.append(utilization_rate)
@@ -707,6 +714,31 @@ class _UtilizationRateAccumulatorMixin(_Accumulator):
                 # f"current_pass_per_layer={[round(x, 2) for x in utilization_rate_tensor.cpu().tolist()]}"
             )
 
+    def _collect_metrics_if_needed(self, gpu_physical_count: torch.Tensor):
+        # sglang:eplb_gpu_physical_count metric is disabled if SGLANG_EPLB_HEATMAP_COLLECTION_INTERVAL <= 0
+        if (
+            envs.SGLANG_EPLB_HEATMAP_COLLECTION_INTERVAL > 0
+            and self._collection_counter % envs.SGLANG_EPLB_HEATMAP_COLLECTION_INTERVAL
+            == 0
+        ):
+            for layer_idx in range(self._expert_location_metadata.num_layers):
+                count_of_layer = (
+                    self._expert_dispatch_collector.eplb_gpu_physical_count.labels(
+                        layer=str(layer_idx)
+                    )
+                )
+                # Exclude the +Inf bucket.
+                assert (
+                    self._expert_location_metadata.ep_size
+                    == len(count_of_layer._buckets) - 1
+                ), f"{self._expert_location_metadata.ep_size=}, {len(count_of_layer._buckets)=}"
+                for gpu_rank in range(self._expert_location_metadata.ep_size):
+                    count = gpu_physical_count[layer_idx, gpu_rank]
+                    if count > 0:
+                        count_of_layer._sum.inc(count * gpu_rank)
+                        count_of_layer._buckets[gpu_rank].inc(count)
+        self._collection_counter += 1
+
 
 class _DequeCollection:
     def __init__(self, maxlens: List[int]):

python/sglang/srt/metrics/collector.py

@@ -999,3 +999,16 @@ class StorageMetricsCollector:
             self._log_histogram(self.histogram_prefetch_bandwidth, v)
         for v in storage_metrics.backup_bandwidth:
             self._log_histogram(self.histogram_backup_bandwidth, v)
+
+
+class ExpertDispatchCollector:
+    def __init__(self, ep_size: int) -> None:
+        from prometheus_client import Histogram
+
+        ep_size_buckets = [i for i in range(ep_size)]
+        self.eplb_gpu_physical_count = Histogram(
+            name="sglang:eplb_gpu_physical_count",
+            documentation="The selected count of physical experts on each layer and GPU rank.",
+            labelnames={"layer"},
+            buckets=ep_size_buckets,
+        )