From b2af34be5404c3ca8f69642ea464470901871711 Mon Sep 17 00:00:00 2001
From: Hubert Lu <55214931+hubertlu-tw@users.noreply.github.com>
Date: Tue, 14 Apr 2026 23:50:32 -0700
Subject: [PATCH] [AMD] Optimize _append_shared_to_topk_output by a single
 fused Triton kernel for Qwen3.5 (#22844)

Co-authored-by: HaiShaw <hixiao@gmail.com>
---
 .../fused_moe_triton_kernels.py               | 76 +++++++++++++++++++
 python/sglang/srt/models/qwen2_moe.py         | 23 +++---
 2 files changed, 86 insertions(+), 13 deletions(-)

diff --git a/python/sglang/srt/layers/moe/fused_moe_triton/fused_moe_triton_kernels.py b/python/sglang/srt/layers/moe/fused_moe_triton/fused_moe_triton_kernels.py
index 2b22f16fe..323d263bf 100644
--- a/python/sglang/srt/layers/moe/fused_moe_triton/fused_moe_triton_kernels.py
+++ b/python/sglang/srt/layers/moe/fused_moe_triton/fused_moe_triton_kernels.py
@@ -1194,3 +1194,79 @@ def fused_append_shared_experts(
         num_warps=1,
     )
     return out_ids, out_weights
+
+
+@triton.jit
+def _fused_append_shared_experts_with_weights_kernel(
+    topk_ids_ptr,
+    topk_weights_ptr,
+    shared_weights_ptr,
+    out_ids_ptr,
+    out_weights_ptr,
+    N_BASE,
+    K: tl.constexpr,
+    S: tl.constexpr,
+    BLOCK_K: tl.constexpr,
+    BLOCK_S: tl.constexpr,
+):
+    pid = tl.program_id(0)
+
+    ids_row_ptr = pid * K
+    out_row_ptr = pid * (K + S)
+
+    offs_k = tl.arange(0, BLOCK_K)
+    mask_k = offs_k < K
+    ids = tl.load(topk_ids_ptr + ids_row_ptr + offs_k, mask=mask_k)
+    ws = tl.load(topk_weights_ptr + ids_row_ptr + offs_k, mask=mask_k)
+
+    tl.store(out_ids_ptr + out_row_ptr + offs_k, ids, mask=mask_k)
+    tl.store(out_weights_ptr + out_row_ptr + offs_k, ws, mask=mask_k)
+
+    offs_s = tl.arange(0, BLOCK_S)
+    mask_s = offs_s < S
+    shared_ids = tl.cast(N_BASE + offs_s, ids.dtype)
+    shared_ws = tl.load(shared_weights_ptr + pid * S + offs_s, mask=mask_s)
+
+    tl.store(out_ids_ptr + out_row_ptr + K + offs_s, shared_ids, mask=mask_s)
+    tl.store(out_weights_ptr + out_row_ptr + K + offs_s, shared_ws, mask=mask_s)
+
+
+def fused_append_shared_experts_with_weights(
+    topk_ids, topk_weights, shared_weights, num_fused_shared_experts, N=None
+):
+    """Like fused_append_shared_experts but accepts per-token shared weights tensor."""
+    assert N is not None, "N (shared expert base id) must be provided"
+    m, k = topk_ids.shape
+    s = int(num_fused_shared_experts)
+    if s <= 0:
+        return topk_ids, topk_weights
+
+    shared_weights_2d = shared_weights.to(topk_weights.dtype)
+    if shared_weights_2d.ndim == 1:
+        shared_weights_2d = shared_weights_2d.unsqueeze(-1)
+    if shared_weights_2d.shape[1] < s:
+        shared_weights_2d = shared_weights_2d.expand(m, s)
+    shared_weights_2d = shared_weights_2d.contiguous()
+
+    out_ids = torch.empty((m, k + s), dtype=topk_ids.dtype, device=topk_ids.device)
+    out_weights = torch.empty(
+        (m, k + s), dtype=topk_weights.dtype, device=topk_weights.device
+    )
+
+    block_k = triton.next_power_of_2(k)
+    block_s = triton.next_power_of_2(s)
+
+    _fused_append_shared_experts_with_weights_kernel[(m,)](
+        topk_ids,
+        topk_weights,
+        shared_weights_2d,
+        out_ids,
+        out_weights,
+        N_BASE=N,
+        K=k,
+        S=s,
+        BLOCK_K=block_k,
+        BLOCK_S=block_s,
+        num_warps=1,
+    )
+    return out_ids, out_weights
diff --git a/python/sglang/srt/models/qwen2_moe.py b/python/sglang/srt/models/qwen2_moe.py
index 35c485de4..1b7348911 100644
--- a/python/sglang/srt/models/qwen2_moe.py
+++ b/python/sglang/srt/models/qwen2_moe.py
@@ -323,20 +323,17 @@ class Qwen2MoeSparseMoeBlock(nn.Module):
         shared_weights = self._get_shared_expert_weights(hidden_states)
         if shared_weights is None:
             return topk_output
-        M = topk_output.topk_ids.shape[0]
-        shared_expert_id = self.num_experts
-        shared_ids = torch.full(
-            (M, self.num_fused_shared_experts),
-            shared_expert_id,
-            dtype=topk_output.topk_ids.dtype,
-            device=topk_output.topk_ids.device,
+
+        from sglang.srt.layers.moe.fused_moe_triton.fused_moe_triton_kernels import (
+            fused_append_shared_experts_with_weights,
         )
-        shared_weights = shared_weights.expand(M, self.num_fused_shared_experts).to(
-            topk_output.topk_weights.dtype
-        )
-        fused_topk_ids = torch.cat([topk_output.topk_ids, shared_ids], dim=-1)
-        fused_topk_weights = torch.cat(
-            [topk_output.topk_weights, shared_weights], dim=-1
+
+        fused_topk_ids, fused_topk_weights = fused_append_shared_experts_with_weights(
+            topk_output.topk_ids,
+            topk_output.topk_weights,
+            shared_weights,
+            self.num_fused_shared_experts,
+            N=self.num_experts,
         )
         return StandardTopKOutput(
             topk_weights=fused_topk_weights,