integrate blockwise fp8 kernel (#3529)

python/pyproject.toml

@@ -25,7 +25,7 @@ runtime_common = [
 ]
 srt = [
     "sglang[runtime_common]", "cuda-python",
-    "sgl-kernel>=0.0.3.post4", "torch", "vllm>=0.6.4.post1,<=0.7.2",
+    "sgl-kernel>=0.0.3.post5", "torch", "vllm>=0.6.4.post1,<=0.7.2",
     "flashinfer_python>=0.2.0.post2", "outlines>=0.0.44,<=0.1.11"
 ]
 

python/sglang/srt/layers/quantization/fp8_kernel.py

@@ -76,11 +76,60 @@ def _per_token_group_quant_fp8(
     tl.store(y_s_ptr, y_s)
 
 
+@triton.jit
+def _per_token_group_quant_fp8_colmajor(
+    # Pointers to inputs and output
+    y_ptr,
+    y_q_ptr,
+    y_s_ptr,
+    group_size,
+    # Num columns of y
+    y_num_columns,
+    # Stride from one column to the next of y_s
+    y_s_col_stride,
+    # Avoid to divide zero
+    eps,
+    # Information for float8
+    fp8_min,
+    fp8_max,
+    # Meta-parameters
+    BLOCK: tl.constexpr,
+):
+    """A Triton-accelerated function to perform per-token-group
+    quantization on a tensor.
+    This function converts the tensor values into float8 values.
+    """
+    # Map the program id to the row of X and Y it should compute.
+    g_id = tl.program_id(0)
+    y_ptr += g_id * group_size
+    y_q_ptr += g_id * group_size
+
+    # Convert g_id the flattened block coordinate to 2D so we can index
+    # into the output y_scales matrix
+    blocks_per_row = y_num_columns // group_size
+    scale_col = g_id % blocks_per_row
+    scale_row = g_id // blocks_per_row
+    y_s_ptr += scale_col * y_s_col_stride + scale_row
+
+    cols = tl.arange(0, BLOCK)  # group_size <= BLOCK
+    mask = cols < group_size
+
+    y = tl.load(y_ptr + cols, mask=mask, other=0.0).to(tl.float32)
+    # Quant
+    _absmax = tl.maximum(tl.max(tl.abs(y)), eps)
+    y_s = _absmax / fp8_max
+    y_q = tl.clamp(y / y_s, fp8_min, fp8_max).to(y_q_ptr.dtype.element_ty)
+
+    tl.store(y_q_ptr + cols, y_q, mask=mask)
+    tl.store(y_s_ptr, y_s)
+
+
 def per_token_group_quant_fp8(
     x: torch.Tensor,
     group_size: int,
     eps: float = 1e-10,
     dtype: torch.dtype = fp8_type_,
+    column_major_scales: bool = False,
 ) -> Tuple[torch.Tensor, torch.Tensor]:
     """Function to perform per-token-group quantization on an input tensor `x`.
 
@@ -112,6 +161,13 @@ def per_token_group_quant_fp8(
     x_q = torch.empty_like(x, device=x.device, dtype=dtype)
     M = x.numel() // group_size
     N = group_size
+    if column_major_scales:
+        x_s = torch.empty(
+            (x.shape[-1] // group_size,) + x.shape[:-1],
+            device=x.device,
+            dtype=torch.float32,
+        ).permute(-1, -2)
+    else:
         x_s = torch.empty(
             x.shape[:-1] + (x.shape[-1] // group_size,),
             device=x.device,
@@ -122,6 +178,22 @@ def per_token_group_quant_fp8(
     # heuristics for number of warps
     num_warps = min(max(BLOCK // 256, 1), 8)
     num_stages = 1
+    if column_major_scales:
+        _per_token_group_quant_fp8_colmajor[(M,)](
+            x,
+            x_q,
+            x_s,
+            group_size,
+            x.shape[1],
+            x_s.stride(1),
+            eps,
+            fp8_min=fp8_min,
+            fp8_max=fp8_max,
+            BLOCK=BLOCK,
+            num_warps=num_warps,
+            num_stages=num_stages,
+        )
+    else:
         _per_token_group_quant_fp8[(M,)](
             x,
             x_q,

python/sglang/srt/layers/quantization/fp8_utils.py

@@ -10,6 +10,9 @@ from sglang.srt.layers.quantization.fp8_kernel import (
 from sglang.srt.utils import is_hip
 
 is_hip_ = is_hip()
+_is_cuda = torch.cuda.is_available() and torch.version.cuda
+if _is_cuda:
+    from sgl_kernel import fp8_blockwise_scaled_mm
 
 
 def normalize_e4m3fn_to_e4m3fnuz(
@@ -36,6 +39,19 @@ def normalize_e4m3fn_to_e4m3fnuz(
     return weight, weight_scale, input_scale
 
 
+def cutlass_block_fp8_supported() -> bool:
+    if _is_cuda:
+        major, minor = torch.cuda.get_device_capability()
+        sm_version = major * 10 + minor
+        cuda_version = tuple(map(int, torch.version.cuda.split(".")))
+        if cuda_version >= (12, 0) and sm_version >= 90:
+            return True
+    return False
+
+
+CUTLASS_BLOCK_FP8_SUPPORTED = cutlass_block_fp8_supported()
+
+
 def apply_w8a8_block_fp8_linear(
     input: torch.Tensor,
     weight: torch.Tensor,
@@ -48,8 +64,21 @@ def apply_w8a8_block_fp8_linear(
     # View input as 2D matrix for fp8 methods
     input_2d = input.view(-1, input.shape[-1])
     output_shape = [*input.shape[:-1], weight.shape[0]]
-
-    q_input, x_scale = per_token_group_quant_fp8(input_2d, block_size[1])
+    # TODO: add more robust shape check here
+    shape_supported_by_cutlass = (
+        weight.shape[0] % 128 == 0 and weight.shape[1] % 128 == 0
+    )
+    if CUTLASS_BLOCK_FP8_SUPPORTED and shape_supported_by_cutlass:
+        q_input, x_scale = per_token_group_quant_fp8(
+            input_2d, block_size[1], column_major_scales=True
+        )
+        output = fp8_blockwise_scaled_mm(
+            q_input, weight.T, x_scale, weight_scale.T, out_dtype=input.dtype
+        )
+    else:
+        q_input, x_scale = per_token_group_quant_fp8(
+            input_2d, block_size[1], column_major_scales=False
+        )
         output = w8a8_block_fp8_matmul(
             q_input, weight, x_scale, weight_scale, block_size, output_dtype=input.dtype
         )