[Bugfix] Enable FP8 KV cache for FlashInfer and Triton backend on non-sm100 GPUs (#24577)

Signed-off-by: Thien Tran <gau.nernst@yahoo.com.sg>

vllm/platforms/cuda.py

@@ -530,6 +530,10 @@ class CudaPlatformBase(Platform):
                     supported = flash_attn_supports_fp8()
                 else:
                     supported = True
+            elif attention_backend == "FLASHINFER":
+                supported = True
+            elif attention_backend == "TRITON_ATTN_VLLM_V1":
+                supported = cls.supports_fp8()
         return supported
 
     @classmethod

vllm/v1/attention/backends/flashinfer.py

@@ -202,7 +202,11 @@ class FlashInferMetadataBuilder(AttentionMetadataBuilder[FlashInferMetadata]):
         else:
             assert self.kv_cache_spec.dtype == self.model_config.dtype
             self.kv_cache_dtype = self.kv_cache_spec.dtype
-        self.q_data_type = self.kv_cache_dtype
+
+        if supports_trtllm_attention()[0]:
+            self.q_data_type = self.kv_cache_dtype
+        else:
+            self.q_data_type = self.model_config.dtype
 
         self._cascade_wrapper = None  # Wrapper for cascade attention