Use Tensor Core Decode when gqa group size >= 4 (#8624)

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

python/sglang/srt/layers/attention/flashinfer_backend.py

@@ -1263,11 +1263,12 @@ def should_use_tensor_core(
     # Calculate GQA group size
     gqa_group_size = num_attention_heads // num_kv_heads
 
-    # Determine based on dtype and GQA group size
+    # For Flashinfer, a GQA group size of at least 4 is needed to efficiently
+    # use Tensor Cores, as it fuses the head group with the token dimension in MMA.
     if kv_cache_dtype in (torch.float8_e4m3fn, torch.float8_e5m2):
         return True
     elif kv_cache_dtype in (torch.float16, torch.half, torch.bfloat16):
-        return gqa_group_size > 4
+        return gqa_group_size >= 4
     else:
         return False