[AMD] Avoid the FP8 wo_a path when the weight is BF16 (#38453)

Signed-off-by: bingxche <bingxche@amd.com>

python/sglang/srt/arg_groups/model_hook.py

@@ -3,7 +3,9 @@
 
 from __future__ import annotations
 
+import json
 import logging
+import os
 from typing import Any
 
 from sglang.srt.arg_groups.overrides import (
@@ -81,6 +83,59 @@ def _rocm_fp8_wo_a_supported() -> bool:
         return False
 
 
+def _probe_wo_a_weight_dtype(model_config: Any, download_dir: str | None) -> str | None:
+    """Read one indexed wo_a dtype without downloading a weight shard."""
+    try:
+        from huggingface_hub import (
+            parse_local_safetensors_file_metadata,
+            parse_safetensors_file_metadata,
+        )
+        from transformers.utils.hub import cached_file
+
+        model_path = model_config.model_path
+        revision = (
+            getattr(model_config.hf_config, "_commit_hash", None)
+            or model_config.revision
+        )
+        index_path = cached_file(
+            model_path,
+            "model.safetensors.index.json",
+            revision=revision,
+            cache_dir=download_dir,
+        )
+        with open(index_path) as f:
+            weight_map = json.load(f).get("weight_map", {})
+        name = next((key for key in weight_map if key.endswith(".wo_a.weight")), None)
+        if name is None:
+            return None
+
+        shard = weight_map[name]
+        local_shard = os.path.join(os.path.dirname(index_path), shard)
+        metadata = (
+            parse_local_safetensors_file_metadata(local_shard)
+            if os.path.isfile(local_shard)
+            else parse_safetensors_file_metadata(model_path, shard, revision=revision)
+        )
+        return getattr(metadata.tensors.get(name), "dtype", None)
+    except Exception:
+        logger.debug("Unable to inspect the checkpoint wo_a dtype", exc_info=True)
+        return None
+
+
+def _configure_rocm_fp8_wo_a_gemm(model_config: Any, download_dir: str | None) -> None:
+    flag = envs.SGLANG_OPT_FP8_WO_A_GEMM
+    if not _rocm_fp8_wo_a_supported():
+        flag.set(False)
+        return
+    if flag.is_set():
+        return
+
+    dtype = _probe_wo_a_weight_dtype(model_config, download_dir)
+    if dtype is not None and dtype != "F8_E4M3":
+        flag.set(False)
+        logger.info("Disabled ROCm fp8 wo_a GEMM for checkpoint dtype %s", dtype)
+
+
 def handle_model_specific_adjustments(server_args: Any):
 
     cfg = resolving_view(server_args)
@@ -387,11 +442,7 @@ def handle_model_specific_adjustments(server_args: Any):
                 envs.SGLANG_OPT_USE_TILELANG_INDEXER.set(True)
         elif get_platform().is_hip:
             envs.SGLANG_OPT_DEEPGEMM_HC_PRENORM.set(False)
-            # The fp8 wo_a GEMM is DeepGEMM-based on CUDA. ROCm has an aiter
-            # e8m0 block-scale equivalent, but only on gfx950 -- everywhere else
-            # keeps the bf16 absorb GEMM.
-            if not _rocm_fp8_wo_a_supported():
-                envs.SGLANG_OPT_FP8_WO_A_GEMM.set(False)
+            _configure_rocm_fp8_wo_a_gemm(model_config, cfg.download_dir)
             envs.SGLANG_OPT_USE_JIT_INDEXER_METADATA.set(False)
             envs.SGLANG_OPT_USE_TOPK_V2.set(True)
             envs.SGLANG_OPT_USE_AITER_INDEXER.set(True)