Add endpoints to dump selected expert ids (#4435)

Co-authored-by: Cheng Wan <54331508+ch-wan@users.noreply.github.com>

docs/backend/native_api.ipynb

@@ -17,6 +17,9 @@
     "- `/update_weights`\n",
     "- `/encode`(embedding model)\n",
     "- `/classify`(reward model)\n",
+    "- `/start_expert_distribution_record`\n",
+    "- `/stop_expert_distribution_record`\n",
+    "- `/dump_expert_distribution_record`\n",
     "\n",
     "We mainly use `requests` to test these APIs in the following examples. You can also use `curl`."
    ]
@@ -362,6 +365,67 @@
     "terminate_process(reward_process)"
    ]
   },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Capture expert selection distribution in MoE models\n",
+    "\n",
+    "SGLang Runtime supports recording the number of times an expert is selected in a MoE model run for each expert in the model. This is useful when analyzing the throughput of the model and plan for optimization."
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "expert_record_server_process, port = launch_server_cmd(\n",
+    "    \"python -m sglang.launch_server --model-path Qwen/Qwen1.5-MoE-A2.7B --host 0.0.0.0\"\n",
+    ")\n",
+    "\n",
+    "wait_for_server(f\"http://localhost:{port}\")"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "response = requests.post(f\"http://localhost:{port}/start_expert_distribution_record\")\n",
+    "print_highlight(response)\n",
+    "\n",
+    "url = f\"http://localhost:{port}/generate\"\n",
+    "data = {\"text\": \"What is the capital of France?\"}\n",
+    "\n",
+    "response = requests.post(url, json=data)\n",
+    "print_highlight(response.json())\n",
+    "\n",
+    "response = requests.post(f\"http://localhost:{port}/stop_expert_distribution_record\")\n",
+    "print_highlight(response)\n",
+    "\n",
+    "response = requests.post(f\"http://localhost:{port}/dump_expert_distribution_record\")\n",
+    "print_highlight(response)\n",
+    "\n",
+    "import glob\n",
+    "\n",
+    "output_file = glob.glob(\"expert_distribution_*.csv\")[0]\n",
+    "with open(output_file, \"r\") as f:\n",
+    "    print_highlight(\"Content of dumped record:\")\n",
+    "    for line in f:\n",
+    "        print_highlight(line.strip())"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "terminate_process(expert_record_server_process)"
+   ]
+  },
   {
    "cell_type": "markdown",
    "metadata": {},

python/sglang/srt/entrypoints/http_server.py

@@ -343,6 +343,36 @@ async def stop_profile_async():
     )
 
 
+@app.api_route("/start_expert_distribution_record", methods=["GET", "POST"])
+async def start_expert_distribution_record_async():
+    """Start recording the expert distribution. Clear the previous record if any."""
+    _global_state.tokenizer_manager.start_expert_distribution_record()
+    return Response(
+        content="Start recording the expert distribution.\n",
+        status_code=200,
+    )
+
+
+@app.api_route("/stop_expert_distribution_record", methods=["GET", "POST"])
+async def stop_expert_distribution_record_async():
+    """Stop recording the expert distribution."""
+    _global_state.tokenizer_manager.stop_expert_distribution_record()
+    return Response(
+        content="Stop recording the expert distribution.\n",
+        status_code=200,
+    )
+
+
+@app.api_route("/dump_expert_distribution_record", methods=["GET", "POST"])
+async def dump_expert_distribution_record_async():
+    """Dump expert distribution record."""
+    _global_state.tokenizer_manager.dump_expert_distribution_record()
+    return Response(
+        content="Dump expert distribution record.\n",
+        status_code=200,
+    )
+
+
 @app.post("/update_weights_from_disk")
 async def update_weights_from_disk(obj: UpdateWeightFromDiskReqInput, request: Request):
     """Update the weights from disk inplace without re-launching the server."""

python/sglang/srt/layers/moe/topk.py

@@ -21,6 +21,10 @@ from sglang.srt.utils import get_compiler_backend, is_cuda
 
 _is_cuda = is_cuda()
 
+from sglang.srt.managers.utils import ExpertDistributionRecorder
+
+expert_distribution_recorder = ExpertDistributionRecorder()
+
 
 def fused_topk_native(
     hidden_states: torch.Tensor,
@@ -223,4 +227,6 @@ def select_experts(
             renormalize=renormalize,
         )
 
+    expert_distribution_recorder.record_new_token(topk_ids)
+
     return topk_weights, topk_ids

python/sglang/srt/managers/io_struct.py

@@ -658,6 +658,12 @@ class ProfileReqType(Enum):
     STOP_PROFILE = 2
 
 
+class ExpertDistributionReq(Enum):
+    START_RECORD = 1
+    STOP_RECORD = 2
+    DUMP_RECORD = 3
+
+
 @dataclass
 class ProfileReq:
     type: ProfileReqType

python/sglang/srt/managers/scheduler.py

@@ -56,6 +56,7 @@ from sglang.srt.layers.logits_processor import LogitsProcessorOutput
 from sglang.srt.managers.io_struct import (
     AbortReq,
     CloseSessionReqInput,
+    ExpertDistributionReq,
     FlushCacheReq,
     GetInternalStateReq,
     GetInternalStateReqOutput,
@@ -104,7 +105,7 @@ from sglang.srt.managers.scheduler_output_processor_mixin import (
 from sglang.srt.managers.session_controller import Session
 from sglang.srt.managers.tp_worker import TpModelWorker
 from sglang.srt.managers.tp_worker_overlap_thread import TpModelWorkerClient
-from sglang.srt.managers.utils import validate_input_length
+from sglang.srt.managers.utils import ExpertDistributionRecorder, validate_input_length
 from sglang.srt.mem_cache.chunk_cache import ChunkCache
 from sglang.srt.mem_cache.hiradix_cache import HiRadixCache
 from sglang.srt.mem_cache.radix_cache import RadixCache
@@ -128,6 +129,8 @@ from sglang.srt.utils import (
 )
 from sglang.utils import TypeBasedDispatcher, get_exception_traceback
 
+expert_distribution_recorder = ExpertDistributionRecorder()
+
 logger = logging.getLogger(__name__)
 
 # Test retract decode for debugging purposes
@@ -403,6 +406,7 @@ class Scheduler(
                 (GetInternalStateReq, self.get_internal_state),
                 (SetInternalStateReq, self.set_internal_state),
                 (RpcReqInput, self.handle_rpc_request),
+                (ExpertDistributionReq, self.expert_distribution_handle),
             ]
         )
 
@@ -1892,6 +1896,16 @@ class Scheduler(
                 ProfileReqOutput(success=True, message="Succeeded.")
             )
 
+    def expert_distribution_handle(self, recv_req: ExpertDistributionReq):
+        if recv_req == ExpertDistributionReq.START_RECORD:
+            expert_distribution_recorder.start_record()
+        elif recv_req == ExpertDistributionReq.STOP_RECORD:
+            expert_distribution_recorder.stop_record()
+        elif recv_req == ExpertDistributionReq.DUMP_RECORD:
+            expert_distribution_recorder.dump_record()
+        else:
+            raise ValueError("Unrecognized ExpertDistributionReq value")
+
     def open_session(self, recv_req: OpenSessionReqInput):
         # handle error
         session_id = recv_req.session_id

python/sglang/srt/managers/tokenizer_manager.py

@@ -60,6 +60,7 @@ from sglang.srt.managers.io_struct import (
     CloseSessionReqInput,
     ConfigureLoggingReq,
     EmbeddingReqInput,
+    ExpertDistributionReq,
     FlushCacheReq,
     GenerateReqInput,
     GetInternalStateReq,
@@ -638,6 +639,18 @@ class TokenizerManager:
         req = ProfileReq(type=ProfileReqType.STOP_PROFILE)
         self.send_to_scheduler.send_pyobj(req)
 
+    def start_expert_distribution_record(self):
+        req = ExpertDistributionReq.START_RECORD
+        self.send_to_scheduler.send_pyobj(req)
+
+    def stop_expert_distribution_record(self):
+        req = ExpertDistributionReq.STOP_RECORD
+        self.send_to_scheduler.send_pyobj(req)
+
+    def dump_expert_distribution_record(self):
+        req = ExpertDistributionReq.DUMP_RECORD
+        self.send_to_scheduler.send_pyobj(req)
+
     async def update_weights_from_disk(
         self,
         obj: UpdateWeightFromDiskReqInput,

python/sglang/srt/managers/utils.py

@@ -1,6 +1,11 @@
+import json
 import logging
+import time
+from collections import defaultdict
 from http import HTTPStatus
-from typing import Optional
+from typing import Dict, List, Optional, Tuple
+
+import torch
 
 from sglang.srt.managers.schedule_batch import FINISH_ABORT, Req
 
@@ -42,3 +47,75 @@ def validate_input_length(
             return error_msg
 
     return None
+
+
+# global expert distribution recording
+class ExpertDistributionRecorder:
+    # This class is a singleton class
+    def __new__(cls):
+        if not hasattr(cls, "instance"):
+            cls.instance = super(ExpertDistributionRecorder, cls).__new__(cls)
+        return cls.instance
+
+    def __init__(self):
+        # the length of the dictionary is the number of layers
+        # the length of the list is the number of tokens
+        # the length of the tuple is topk's k value
+        self._expert_distribution_record: Dict[int, List[Tuple[int]]] = defaultdict(
+            list
+        )
+        self._record = False
+        self._current_layer_id = "UNKNOWN"
+
+    def set_current_layer(self, layer_idx):
+        self._current_layer_id = layer_idx
+
+    def record_new_token(self, topk_ids):
+        if not self._record:
+            return
+        topk_ids_list = topk_ids.to("cpu", non_blocking=True).numpy().tolist()
+        torch.cuda.synchronize()
+        for i in topk_ids_list:
+            self._expert_distribution_record[self._current_layer_id].append(tuple(i))
+
+    def reset(self):
+        """Reset the expert distribution recorder."""
+        logger.info("Resetting expert distribution record...")
+        self._record = False
+        self._expert_distribution_record.clear()
+        self._current_layer_id = "UNKNOWN"
+
+    def start_record(self):
+        """Start recording the expert distribution. Reset the recorder and set the recording flag to True."""
+        if self._record == True:
+            logger.warning(
+                "SGLang server is already recording expert ids. Did you forget to dump the expert ids recorded so far by sending requests to the `/stop_expert_distribution_record` and `/dump_expert_distribution_record` endpoints?"
+            )
+        self.reset()
+        self._record = True
+
+    def stop_record(self):
+        """Stop recording the expert distribution. Set the recording flag to False."""
+        if self._record == False:
+            logger.warning(
+                "SGLang server has not been recording expert ids. Did you forget to start recording by sending request to the `/start_expert_distribution_record` endpoint?"
+            )
+        self._record = False
+
+    def dump_record(self):
+        """Dump the expert distribution record to a file. Reset the recorder after dumping."""
+        results = {}
+        for layer_idx, layer_record in self._expert_distribution_record.items():
+            results[layer_idx] = defaultdict(int)
+            for token_record in layer_record:
+                for expert_idx in token_record:
+                    results[layer_idx][expert_idx] += 1
+        with open(
+            f"expert_distribution_rank{torch.distributed.get_rank()}_timestamp{time.time()}.csv",
+            "w",
+        ) as fd:
+            fd.write("layer_id,expert_id,count\n")
+            for layer_idx, layer_results in results.items():
+                for expert_idx, count in layer_results.items():
+                    fd.write(f"{layer_idx},{expert_idx},{count}\n")
+        self.reset()

python/sglang/srt/models/deepseek_v2.py

@@ -68,6 +68,7 @@ from sglang.srt.layers.vocab_parallel_embedding import (
     VocabParallelEmbedding,
 )
 from sglang.srt.managers.schedule_batch import global_server_args_dict
+from sglang.srt.managers.utils import ExpertDistributionRecorder
 from sglang.srt.model_executor.forward_batch_info import ForwardBatch, ForwardMode
 from sglang.srt.model_loader.weight_utils import default_weight_loader
 from sglang.srt.utils import add_prefix, is_cuda, is_cuda_available, is_hip
@@ -80,6 +81,8 @@ if _is_cuda:
 else:
     from vllm import _custom_ops as ops
 
+expert_distribution_recorder = ExpertDistributionRecorder()
+
 
 class DeepseekV2MLP(nn.Module):
     def __init__(
@@ -1160,6 +1163,7 @@ class DeepseekV2Model(nn.Module):
 
         residual = None
         for i in range(len(self.layers)):
+            expert_distribution_recorder.set_current_layer(i)
             layer = self.layers[i]
             hidden_states, residual = layer(
                 positions, hidden_states, forward_batch, residual

test/srt/run_suite.py

@@ -30,6 +30,7 @@ suites = {
         TestFile("test_ebnf_constrained.py"),
         TestFile("test_fp8_kernel.py", 2),
         TestFile("test_embedding_openai_server.py", 36),
+        TestFile("test_expert_distribution.py", 31),
         TestFile("test_gguf.py", 78),
         TestFile("test_gptqmodel_dynamic.py", 72),
         TestFile("test_hidden_states.py", 55),

test/srt/test_expert_distribution.py

@@ -0,0 +1,111 @@
+import csv
+import glob
+import os
+import unittest
+
+import requests
+
+from sglang.srt.utils import kill_process_tree
+from sglang.test.test_utils import (
+    DEFAULT_SMALL_MOE_MODEL_NAME_FOR_TEST,
+    DEFAULT_TIMEOUT_FOR_SERVER_LAUNCH,
+    DEFAULT_URL_FOR_TEST,
+    popen_launch_server,
+)
+
+
+class TestExpertDistribution(unittest.TestCase):
+    def setUp(self):
+        # Clean up any existing expert distribution files before each test
+        for f in glob.glob("expert_distribution_*.csv"):
+            os.remove(f)
+
+    def tearDown(self):
+        # Clean up any expert distribution files after each test
+        for f in glob.glob("expert_distribution_*.csv"):
+            os.remove(f)
+
+    def test_expert_distribution_record(self):
+        """Test expert distribution record endpoints"""
+        process = popen_launch_server(
+            DEFAULT_SMALL_MOE_MODEL_NAME_FOR_TEST,
+            DEFAULT_URL_FOR_TEST,
+            timeout=DEFAULT_TIMEOUT_FOR_SERVER_LAUNCH,
+        )
+
+        try:
+            # Start recording
+            response = requests.post(
+                f"{DEFAULT_URL_FOR_TEST}/start_expert_distribution_record"
+            )
+            self.assertEqual(response.status_code, 200)
+
+            # Make some requests to generate expert distribution data
+            response = requests.post(
+                f"{DEFAULT_URL_FOR_TEST}/generate",
+                json={
+                    "text": "The capital of France is",
+                    "sampling_params": {
+                        "temperature": 0,
+                        "max_new_tokens": 32,
+                    },
+                },
+            )
+            self.assertEqual(response.status_code, 200)
+
+            # Stop recording
+            response = requests.post(
+                f"{DEFAULT_URL_FOR_TEST}/stop_expert_distribution_record"
+            )
+            self.assertEqual(response.status_code, 200)
+
+            # Dump the recorded data
+            response = requests.post(
+                f"{DEFAULT_URL_FOR_TEST}/dump_expert_distribution_record"
+            )
+            self.assertEqual(response.status_code, 200)
+
+            # Verify the dumped file exists and has correct format
+            csv_files = glob.glob("expert_distribution_*.csv")
+            self.assertEqual(
+                len(csv_files), 1, "Expected exactly one expert distribution CSV file"
+            )
+
+            # Check CSV file format
+            with open(csv_files[0], "r") as f:
+                csv_reader = csv.reader(f)
+
+                # Check header
+                header = next(csv_reader)
+                self.assertEqual(
+                    header,
+                    ["layer_id", "expert_id", "count"],
+                    "CSV header should be 'layer_id,expert_id,count'",
+                )
+
+                # Check data rows
+                rows = list(csv_reader)
+                self.assertGreater(len(rows), 0, "CSV file should contain data rows")
+
+                for row in rows:
+                    # Verify each row has 3 columns
+                    self.assertEqual(
+                        len(row),
+                        3,
+                        "Each row should have layer_id, expert_id and count",
+                    )
+
+                    # Verify data types
+                    layer_id, expert_id, count = row
+                    self.assertTrue(layer_id.isdigit(), "layer_id should be an integer")
+                    self.assertTrue(
+                        expert_id.isdigit(), "expert_id should be an integer"
+                    )
+                    self.assertTrue(count.isdigit(), "count should be an integer")
+
+        finally:
+            kill_process_tree(process.pid)
+
+
+if __name__ == "__main__":
+    unittest.main()