Fix the FP8 E4M3 parsing offline scales failure bug (#3045)

python/sglang/srt/model_loader/weight_utils.py

@@ -27,6 +27,7 @@ import huggingface_hub.constants
 import numpy as np
 import torch
 from huggingface_hub import HfFileSystem, hf_hub_download, snapshot_download
+from pydantic import BaseModel, ConfigDict, ValidationInfo, model_validator
 from safetensors.torch import load_file, safe_open, save_file
 from tqdm.auto import tqdm
 
@@ -650,6 +651,81 @@ def maybe_remap_kv_scale_name(name: str, params_dict: dict) -> Optional[str]:
     return name
 
 
+# Adapted from https://github.com/vllm-project/vllm/blob/68ad4e3a8d8a66fb2a43be57471ee13a8bec4ec0/vllm/model_executor/layers/quantization/schema.py
+class KVCacheQuantSchema(BaseModel):
+    dtype: str
+    # Each key is a TP rank. Each value is a dictionary mapping a TP rank's
+    # layer indices to their per-tensor KV cache scaling factor.
+    # TODO: Consider pulling this and its validation methods out into its
+    # own schema class (tricky as its members are variable)
+    scaling_factor: Dict[int, Dict[int, float]]
+
+    @model_validator(mode="after")
+    def check_is_fp8(self) -> "KVCacheQuantSchema":
+        assert self.dtype == "float8_e4m3fn", (
+            "Loaded scaling factors intended for KV cache dtype = "
+            f"{self.dtype} rather than float8_e4m3fn!"
+        )
+        return self
+
+    @model_validator(mode="after")
+    def check_tp_ranks(self, info: ValidationInfo) -> "KVCacheQuantSchema":
+        context = info.context
+        if context:
+            tp_size = context["tp_size"]
+            num_hidden_layers = context["num_hidden_layers"]
+            assert len(self.scaling_factor) == tp_size, (
+                f"Loaded dictionary has TP size {len(self.scaling_factor)} "
+                f"but LLM engine is currently running with TP size {tp_size}."
+            )
+            for tp_rank, layer_maps in self.scaling_factor.items():
+                assert len(layer_maps) == num_hidden_layers, (
+                    f"KV cache scales map for TP rank {tp_rank} is malformed. "
+                    f"Expected {num_hidden_layers} layers, got "
+                    f"{len(layer_maps)}."
+                )
+            for i in range(tp_size):
+                assert (
+                    i in self.scaling_factor
+                ), f"KV cache scales map for TP rank {i} not found."
+        return self
+
+    @model_validator(mode="after")
+    def check_current_rank(self, info: ValidationInfo) -> "KVCacheQuantSchema":
+        context = info.context
+        if context:
+            tp_rank = context["tp_rank"]
+            num_hidden_layers = context["num_hidden_layers"]
+            layer_scales_map = self.scaling_factor[tp_rank]
+            for i in range(num_hidden_layers):
+                assert i in layer_scales_map, (
+                    f"Could not find KV cache scales for layer {i} in "
+                    f"TP rank {tp_rank}."
+                )
+        return self
+
+
+class QuantParamSchema(BaseModel):
+    # TODO: Generalize and extend with more fields
+    # (e.g. weights/activations params) once functionality is enabled
+    model_config = ConfigDict(protected_namespaces=())
+    model_type: Optional[str]
+    kv_cache: KVCacheQuantSchema
+
+    @model_validator(mode="after")
+    def check_model_type(self, info: ValidationInfo) -> "QuantParamSchema":
+        context = info.context
+        if context:
+            model_type = context.get("model_type", None)
+            if model_type is not None:
+                assert model_type == self.model_type, (
+                    f"Model type is {model_type} but loaded "
+                    f"scaling factors belonging to different "
+                    f"model type {self.model_type}!"
+                )
+        return self
+
+
 def kv_cache_scales_loader(
     filename: str,
     tp_rank: int,
@@ -681,7 +757,7 @@ def kv_cache_scales_loader(
     except json.JSONDecodeError:
         logger.error("Error decoding JSON in file '%s'.", filename)
     except Exception:
-        logger.exception("An error occurred while reading '%s'.", filename)
+        logger.error("An error occurred while reading '%s'.", filename)
     # This section is reached if and only if any of the excepts are hit
     # Return an empty iterable (list) => no KV cache scales are loaded
     # which ultimately defaults to 1.0 scales