[Perf] Improve default triton fused moe configs (#34846)

Signed-off-by: mgoin <mgoin64@gmail.com>
Co-authored-by: Robert Shaw <114415538+robertgshaw2-redhat@users.noreply.github.com>

benchmarks/kernels/benchmark_moe_defaults.py

+#!/usr/bin/env python3
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+"""
+Benchmark comparing old vs new default fused MoE configs.
+
+Runs the triton fused_moe kernel with three configurations for each scenario:
+  1. Tuned config (from JSON file, if available) — the target to match
+  2. Old default (the hardcoded defaults before this change)
+  3. New default (the improved defaults)
+
+Usage:
+    python benchmarks/kernels/benchmark_moe_defaults.py
+
+Produces a table showing kernel time (us) and speedup of new vs old defaults.
+"""
+
+import torch
+
+from vllm.model_executor.layers.fused_moe import fused_topk, override_config
+from vllm.model_executor.layers.fused_moe.config import FusedMoEQuantConfig
+from vllm.model_executor.layers.fused_moe.fused_moe import (
+    fused_experts,
+    get_default_config,
+    get_moe_configs,
+)
+from vllm.platforms import current_platform
+from vllm.triton_utils import triton
+from vllm.utils.torch_utils import set_random_seed
+
+FP8_DTYPE = current_platform.fp8_dtype()
+
+
+def old_default_config(M, E, N, K, topk, dtype=None, block_shape=None):
+    """The original defaults before https://github.com/vllm-project/vllm/pull/34846,
+    for comparison."""
+    if dtype == "fp8_w8a8" and block_shape is not None:
+        return {
+            "BLOCK_SIZE_M": 64,
+            "BLOCK_SIZE_N": block_shape[0],
+            "BLOCK_SIZE_K": block_shape[1],
+            "GROUP_SIZE_M": 32,
+            "SPLIT_K": 1,
+            "num_warps": 4,
+            "num_stages": 3 if not current_platform.is_rocm() else 2,
+        }
+    elif M <= E:
+        return {
+            "BLOCK_SIZE_M": 16,
+            "BLOCK_SIZE_N": 32,
+            "BLOCK_SIZE_K": 64,
+            "GROUP_SIZE_M": 1,
+            "SPLIT_K": 1,
+        }
+    else:
+        return {
+            "BLOCK_SIZE_M": 64,
+            "BLOCK_SIZE_N": 64,
+            "BLOCK_SIZE_K": 32,
+            "GROUP_SIZE_M": 8,
+            "SPLIT_K": 1,
+        }
+
+
+def benchmark_config(
+    config,
+    M,
+    E,
+    N,
+    K,
+    topk,
+    dtype,
+    use_fp8=False,
+    block_shape=None,
+    num_iters=100,
+):
+    """Time a single kernel config. Returns kernel time in microseconds."""
+    init_dtype = torch.float16 if use_fp8 else dtype
+
+    a = torch.randn(M, K, device="cuda", dtype=init_dtype) / 10
+    w1 = torch.randn(E, 2 * N, K, device="cuda", dtype=init_dtype) / 10
+    w2 = torch.randn(E, K, N, device="cuda", dtype=init_dtype) / 10
+
+    w1_scale = None
+    w2_scale = None
+    a1_scale = None
+    a2_scale = None
+    if use_fp8:
+        if block_shape is not None:
+            bsn, bsk = block_shape
+            n_tiles_w1 = triton.cdiv(2 * N, bsn)
+            k_tiles_w1 = triton.cdiv(K, bsk)
+            n_tiles_w2 = triton.cdiv(K, bsn)
+            k_tiles_w2 = triton.cdiv(N, bsk)
+            w1_scale = torch.rand(
+                E, n_tiles_w1, k_tiles_w1, device="cuda", dtype=torch.float32
+            )
+            w2_scale = torch.rand(
+                E, n_tiles_w2, k_tiles_w2, device="cuda", dtype=torch.float32
+            )
+        else:
+            w1_scale = torch.rand(E, device="cuda", dtype=torch.float32)
+            w2_scale = torch.rand(E, device="cuda", dtype=torch.float32)
+        a1_scale = torch.rand(1, device="cuda", dtype=torch.float32)
+        a2_scale = torch.rand(1, device="cuda", dtype=torch.float32)
+        # Only weights are stored in fp8; activations stay in bf16/fp16
+        # and get dynamically quantized inside the kernel.
+        w1 = w1.to(FP8_DTYPE)
+        w2 = w2.to(FP8_DTYPE)
+
+    quant_config = FusedMoEQuantConfig.make(
+        quant_dtype=torch.float8_e4m3fn if use_fp8 else None,
+        w1_scale=w1_scale,
+        w2_scale=w2_scale,
+        a1_scale=a1_scale,
+        a2_scale=a2_scale,
+        block_shape=block_shape,
+    )
+
+    gating = torch.randn(M, E, device="cuda", dtype=torch.float32)
+
+    # Warmup
+    for _ in range(20):
+        with override_config(config):
+            topk_weights, topk_ids, _ = fused_topk(a, gating, topk, renormalize=True)
+            fused_experts(
+                a,
+                w1,
+                w2,
+                topk_weights,
+                topk_ids,
+                quant_config=quant_config,
+            )
+    torch.cuda.synchronize()
+
+    # Benchmark
+    start = torch.cuda.Event(enable_timing=True)
+    end = torch.cuda.Event(enable_timing=True)
+    start.record()
+    for _ in range(num_iters):
+        with override_config(config):
+            topk_weights, topk_ids, _ = fused_topk(a, gating, topk, renormalize=True)
+            fused_experts(
+                a,
+                w1,
+                w2,
+                topk_weights,
+                topk_ids,
+                quant_config=quant_config,
+            )
+    end.record()
+    torch.cuda.synchronize()
+    return start.elapsed_time(end) / num_iters * 1000  # ms -> us
+
+
+# Model configurations: (name, E, N, K, topk, dtype_str, use_fp8, block_shape)
+# N = moe_intermediate_size // tp_size (the value used in config file lookup)
+MODELS = [
+    # --- Few experts ---
+    ("Mixtral bf16", 8, 7168, 4096, 2, None, False, None),
+    ("Mixtral fp8", 8, 7168, 4096, 2, "fp8_w8a8", True, None),
+    # --- Many experts: real model shapes at tp=1 ---
+    # Qwen2-MoE-57B: E=60, topk=4, N=1408, K=2048
+    ("Qwen2-MoE bf16", 60, 1408, 2048, 4, None, False, None),
+    # DeepSeek-V2: E=64, topk=6, N=1407, K=4096
+    # (use 1408 to avoid odd alignment; real model is 1407)
+    ("DeepSeek-V2 bf16", 64, 1408, 4096, 6, None, False, None),
+    # OLMoE-7B: E=64, topk=8, N=2048, K=2048
+    ("OLMoE bf16", 64, 2048, 2048, 8, None, False, None),
+    # GLM-4-100B-A10B: E=128, topk=8, N=1408, K=4096
+    ("GLM-4-MoE bf16", 128, 1408, 4096, 8, None, False, None),
+    # Qwen3-30B-A3B: E=128, topk=8, N=768, K=2048
+    ("Qwen3-MoE bf16", 128, 768, 2048, 8, None, False, None),
+    # DeepSeek-V3 / MiMo-V2-Flash: E=256, topk=8, N=2048, K=7168
+    ("DeepSeek-V3 bf16", 256, 2048, 7168, 8, None, False, None),
+    # Qwen3.5-70B-A22B (Qwen3-Next): E=512, topk=10, N=512, K=2048
+    ("Qwen3-Next bf16", 512, 512, 2048, 10, None, False, None),
+    # E=128 N=1856 bf16
+    ("E128 N1856 bf16", 128, 1856, 4096, 8, None, False, None),
+    # E=256 N=512 bf16 (DS-V3 tp=4)
+    ("DS-V3 tp4 bf16", 256, 512, 7168, 8, None, False, None),
+    # E=512 N=512 bf16 (Qwen3-Next tp=1)
+    ("Qwen3-Next bf16", 512, 512, 2048, 10, None, False, None),
+    # E=512 N=256 bf16 (Qwen3-Next tp=2)
+    ("Qwen3-Next tp2", 512, 256, 2048, 10, None, False, None),
+    # --- FP8 block quant (many experts) ---
+    # DS-V3 tp=4: E=256, N=512, fp8 block
+    ("DS-V3 tp4 fp8blk", 256, 512, 7168, 8, "fp8_w8a8", True, [128, 128]),
+    # DS-V3 tp=8: E=256, N=256, fp8 block
+    ("DS-V3 tp8 fp8blk", 256, 256, 7168, 8, "fp8_w8a8", True, [128, 128]),
+    # Qwen3-Next tp=2 fp8 block
+    ("Qwen3-Next tp2 fp8blk", 512, 256, 2048, 10, "fp8_w8a8", True, [128, 128]),
+]
+
+BATCH_SIZES = [1, 4, 8, 16, 32, 64, 128, 256, 512, 1024, 2048, 4096]
+
+
+def main():
+    set_random_seed(0)
+    torch.set_default_device("cuda")
+    dtype = torch.bfloat16
+
+    for name, E, N, K, topk, dtype_str, use_fp8, block_shape in MODELS:
+        print(f"\n{'=' * 90}")
+        print(f"  {name}  (E={E}, N={N}, K={K}, topk={topk})")
+        print(f"{'=' * 90}")
+
+        # Try to load tuned config
+        block_n = block_shape[0] if block_shape else None
+        block_k = block_shape[1] if block_shape else None
+        tuned = get_moe_configs(E, N, dtype_str, block_n, block_k)
+        has_tuned = tuned is not None
+        print(f"  Tuned config available: {has_tuned}")
+
+        hdr = (
+            f"{'Batch':>6} | {'Tuned (us)':>11} | {'Old (us)':>11} | "
+            f"{'New (us)':>11} | {'New/Old':>8} | {'New/Tuned':>10}"
+        )
+        print(f"  {hdr}")
+        print(f"  {'-' * len(hdr)}")
+
+        for M in BATCH_SIZES:
+            old_cfg = old_default_config(M, E, N, K, topk, dtype_str, block_shape)
+            new_cfg = get_default_config(M, E, N, K, topk, dtype_str, block_shape)
+
+            if has_tuned:
+                tuned_cfg = tuned[min(tuned.keys(), key=lambda x: abs(x - M))]
+                t_tuned = benchmark_config(
+                    tuned_cfg,
+                    M,
+                    E,
+                    N,
+                    K,
+                    topk,
+                    dtype,
+                    use_fp8=use_fp8,
+                    block_shape=block_shape,
+                )
+            else:
+                t_tuned = None
+
+            t_old = benchmark_config(
+                old_cfg,
+                M,
+                E,
+                N,
+                K,
+                topk,
+                dtype,
+                use_fp8=use_fp8,
+                block_shape=block_shape,
+            )
+            t_new = benchmark_config(
+                new_cfg,
+                M,
+                E,
+                N,
+                K,
+                topk,
+                dtype,
+                use_fp8=use_fp8,
+                block_shape=block_shape,
+            )
+
+            ratio_new_old = t_new / t_old
+            tuned_str = f"{t_tuned:11.2f}" if t_tuned else f"{'N/A':>11}"
+            ratio_tuned = f"{t_new / t_tuned:10.2f}x" if t_tuned else f"{'N/A':>10}"
+            # flag regressions where new default is >5% slower than old
+            marker = " <--" if ratio_new_old > 1.05 else ""
+
+            print(
+                f"  {M:>6} | {tuned_str} | {t_old:11.2f} | {t_new:11.2f} "
+                f"| {ratio_new_old:7.2f}x | {ratio_tuned}{marker}"
+            )
+
+
+if __name__ == "__main__":
+    main()

vllm/model_executor/layers/fused_moe/fused_moe.py

@@ -1233,28 +1233,31 @@ def get_default_config(
     block_shape: list[int] | None = None,
 ) -> dict[str, int]:
     if vllm_is_batch_invariant():
-        config = {
+        return {
             "BLOCK_SIZE_M": 64,
             "BLOCK_SIZE_N": 64,
             "BLOCK_SIZE_K": 32,
             "GROUP_SIZE_M": 8,
             "SPLIT_K": 1,
         }
-        return config
+
+    # num_stages can cause triton.runtime.errors.OutOfResources on ROCm.
+    num_stages_rocm = 2
 
     if dtype == "fp8_w8a8" and block_shape is not None:
-        # Block-wise quant: BLOCK_SIZE_N must be divisible by block_shape[0]
-        # BLOCK_SIZE_K must be divisible by block_shape[1]
-        # num_stages=3 can cause triton.runtime.errors.OutOfResources
-        # on ROCm, set it to 2 instead.
+        # Block-wise quant: tile sizes are constrained by block_shape.
+        # Use a small M tile for decode-like batches where tokens are
+        # spread thin across experts. Larger batches benefit from
+        # GROUP_SIZE_M > 1 because the per-block scales add memory
+        # traffic that benefits from L2 tile reuse.
         config = {
-            "BLOCK_SIZE_M": 64,
+            "BLOCK_SIZE_M": 16 if M <= 64 else 64,
             "BLOCK_SIZE_N": block_shape[0],
             "BLOCK_SIZE_K": block_shape[1],
-            "GROUP_SIZE_M": 32,
+            "GROUP_SIZE_M": 1 if M <= 16 else 32,
             "SPLIT_K": 1,
             "num_warps": 4,
-            "num_stages": 3 if not current_platform.is_rocm() else 2,
+            "num_stages": 3 if not current_platform.is_rocm() else num_stages_rocm,
         }
     elif dtype in ["int4_w4a16", "int8_w8a16"] and block_shape is not None:
         # moe wna16 kernels
@@ -1270,21 +1273,52 @@ def get_default_config(
             config = {"BLOCK_SIZE_M": 32, "GROUP_SIZE_M": 1, "SPLIT_K": 1}
         else:
             config = {"BLOCK_SIZE_M": 64, "GROUP_SIZE_M": 1, "SPLIT_K": 1}
-    elif M <= E:
-        config = {
-            "BLOCK_SIZE_M": 16,
-            "BLOCK_SIZE_N": 32,
-            "BLOCK_SIZE_K": 64,
-            "GROUP_SIZE_M": 1,
-            "SPLIT_K": 1,
-        }
     else:
+        # General defaults for bf16/fp16 and fp8 per-tensor.
+        # Tile sizes scale with batch: small batches are memory-bound
+        # (favor tall-K tiles), large batches are compute-bound (favor
+        # large M/N tiles with more warps).
+        if M <= 32:
+            block_m = 16
+        elif M <= 96:
+            block_m = 32
+        elif M <= 512:
+            block_m = 64
+        else:
+            block_m = 128
+
+        block_n = 64 if M <= 64 else 128
+
+        # Small batches benefit from longer reduction (larger K tile),
+        # while large batches prefer more output parallelism.
+        # FP8 elements are half-width so larger K tiles are always cheap.
+        block_k = 128 if dtype == "fp8_w8a8" or M <= 64 else 64
+
+        # Grouping adjacent M-blocks lets them share weight tiles in L2.
+        # Only helps when there are enough M-blocks per expert to group;
+        # with many experts each one sees few tokens so grouping is useless.
+        tokens_per_expert = M // max(E, 1)
+        group_m = 16 if tokens_per_expert > 128 else 1
+
+        # Large batches have enough blocks to saturate the GPU, so we
+        # use more warps per block to increase arithmetic intensity.
+        num_warps = 4 if M <= 128 else 8
+
+        if current_platform.is_rocm():
+            num_stages = num_stages_rocm
+        elif M <= 32:
+            num_stages = 4
+        else:
+            num_stages = 3
+
         config = {
-            "BLOCK_SIZE_M": 64,
-            "BLOCK_SIZE_N": 64,
-            "BLOCK_SIZE_K": 32,
-            "GROUP_SIZE_M": 8,
+            "BLOCK_SIZE_M": block_m,
+            "BLOCK_SIZE_N": block_n,
+            "BLOCK_SIZE_K": block_k,
+            "GROUP_SIZE_M": group_m,
             "SPLIT_K": 1,
+            "num_warps": num_warps,
+            "num_stages": num_stages,
         }
     return config