Support getting checksums in weight checker (#24537)

python/sglang/srt/entrypoints/http_server.py

@@ -1295,11 +1295,13 @@ async def resume_memory_occupation(
 @app.post("/weights_checker")
 @auth_level(AuthLevel.ADMIN_OPTIONAL)
 async def check_weights(obj: CheckWeightsReqInput, request: Request):
-    success, message = await _global_state.tokenizer_manager.check_weights(obj, request)
-    return ORJSONResponse(
-        {"success": success, "message": message},
-        status_code=200 if success else HTTPStatus.BAD_REQUEST,
+    success, message, ranks = await _global_state.tokenizer_manager.check_weights(
+        obj, request
     )
+    body = {"success": success, "message": message}
+    if ranks is not None:
+        body["ranks"] = ranks
+    return ORJSONResponse(body, status_code=200 if success else HTTPStatus.BAD_REQUEST)
 
 
 @app.api_route("/slow_down", methods=["GET", "POST"])

python/sglang/srt/managers/io_struct.py

@@ -1625,6 +1625,7 @@ class CheckWeightsReqInput(BaseReq):
 class CheckWeightsReqOutput(BaseReq):
     success: bool
     message: str
+    payload: Optional[Dict] = None
 
 
 @dataclass

python/sglang/srt/managers/scheduler_update_weights_mixin.py

@@ -196,8 +196,10 @@ class SchedulerUpdateWeightsMixin:
 
     def check_weights(self: Scheduler, recv_req: CheckWeightsReqInput):
         try:
-            self.tp_worker.model_runner.check_weights(action=recv_req.action)
-            return CheckWeightsReqOutput(success=True, message="Success.")
+            payload = self.tp_worker.model_runner.check_weights(action=recv_req.action)
+            return CheckWeightsReqOutput(
+                success=True, message="Success.", payload=payload
+            )
         except Exception as e:
             logger.warning(f"check_weights see error: {e}")
             traceback.print_exc()

python/sglang/srt/managers/tokenizer_control_mixin.py

@@ -764,10 +764,14 @@ class TokenizerControlMixin:
         self: TokenizerManager,
         obj: CheckWeightsReqInput,
         request: Optional[fastapi.Request] = None,
-    ) -> CheckWeightsReqOutput:
+    ) -> Tuple[bool, str, Optional[List[Dict]]]:
         self.auto_create_handle_loop()
         results = await self.check_weights_communicator(obj)
-        return FanOutCommunicator.merge_results(results)
+        success, message = FanOutCommunicator.merge_results(results)
+        ranks: Optional[List[Dict]] = None
+        if any(r.payload is not None for r in results):
+            ranks = [r.payload for r in results]
+        return success, message, ranks
 
     async def slow_down(
         self: TokenizerManager,

python/sglang/srt/model_executor/model_runner.py

@@ -3484,7 +3484,7 @@ class ModelRunner(ModelRunnerKVCacheMixin):
         ShardedStateLoader.save_model(self.model, path, pattern, max_size)
 
     def check_weights(self, action: str):
-        self._weight_checker.handle(action=action)
+        return self._weight_checker.handle(action=action)
 
     def update_weights_from_ipc(self, recv_req):
         """Update weights from IPC for checkpoint-engine integration."""

python/sglang/srt/utils/weight_checker.py

@@ -1,16 +1,40 @@
 import logging
-from typing import Dict, Iterable, Tuple
+import time
+from typing import Dict, Iterable, Optional, Tuple
 
 import torch
+import torch.distributed as dist
+from pydantic import BaseModel, ConfigDict
 
 from sglang.srt.layers.quantization.fp8_utils import (
     block_quant_dequant,
     inverse_transform_scale_ue8m0,
 )
+from sglang.srt.managers.mm_utils import tensor_hash
 
 logger = logging.getLogger(__name__)
 
 
+class _StrictBaseModel(BaseModel):
+    model_config = ConfigDict(extra="forbid")
+
+
+class ParallelismInfo(_StrictBaseModel):
+    tp_rank: int
+    tp_size: int
+    dp_rank: int
+    dp_size: int
+    pp_rank: int
+    pp_size: int
+    rank: int
+    size: int
+
+
+class ChecksumInfo(_StrictBaseModel):
+    checksums: Dict[str, str]
+    parallelism_info: ParallelismInfo
+
+
 _NON_PERSISTENT_BUFFER_PATTERNS = (
     "cos_sin_cache",
     "inv_freq",
@@ -28,14 +52,16 @@ class WeightChecker:
         self._model_runner = model_runner
         self._snapshot_tensors = None
 
-    def handle(self, action: str):
+    def handle(self, action: str) -> Optional[Dict]:
         logger.info(f"[WeightChecker] handle action={action}")
         if action == "snapshot":
-            self._snapshot()
+            return self._snapshot()
         elif action == "reset_tensors":
-            self._reset_tensors()
+            return self._reset_tensors()
         elif action == "compare":
-            self._compare()
+            return self._compare()
+        elif action == "checksum":
+            return self._compute_checksum()
         else:
             raise Exception(f"Unsupported {action=}")
 
@@ -62,12 +88,56 @@ class WeightChecker:
             actual_tensors=_postprocess_tensors(dict(self._model_state())),
         )
 
+    def _compute_checksum(self) -> Dict:
+        torch.cuda.synchronize()
+        start = time.perf_counter()
+
+        # Reuse the snapshot/compare postprocess pipeline so fp8 weights are
+        # dequantized to bf16 before hashing — two (qweight, scale) pairs that
+        # produce the same bf16 must produce the same checksum.
+        checksums = {
+            name: _hash_tensor(tensor.data)
+            for name, should_compare, tensor in _postprocess_tensors(
+                dict(self._model_state())
+            )
+            if should_compare
+        }
+
+        torch.cuda.synchronize()
+        elapsed = time.perf_counter() - start
+        logger.info(
+            f"[WeightChecker] checksum computed for {len(checksums)} tensors in {elapsed:.3f}s"
+        )
+
+        info = ChecksumInfo(
+            checksums=checksums,
+            parallelism_info=self._parallelism_info(),
+        )
+        return info.model_dump()
+
+    def _parallelism_info(self) -> ParallelismInfo:
+        mr = self._model_runner
+        return ParallelismInfo(
+            tp_rank=mr.tp_rank,
+            tp_size=mr.tp_size,
+            dp_rank=mr.dp_rank if mr.dp_rank is not None else 0,
+            dp_size=mr.dp_size,
+            pp_rank=mr.pp_rank,
+            pp_size=mr.pp_size,
+            rank=dist.get_rank() if dist.is_initialized() else 0,
+            size=dist.get_world_size() if dist.is_initialized() else 1,
+        )
+
     def _model_state(self):
         # TODO: support EAGLE etc (e.g. yield from both main model and draft model)
         yield from self._model_runner.model.named_parameters()
         yield from self._model_runner.model.named_buffers()
 
 
+def _hash_tensor(t: torch.Tensor) -> str:
+    return f"{tensor_hash(t):016x}"
+
+
 def _check_tensors(
     expect_tensors: Iterable[Tuple[str, bool, torch.Tensor]],
     actual_tensors: Iterable[Tuple[str, bool, torch.Tensor]],