From 733a0c1a377132b64d58777eedaabf3b46229f72 Mon Sep 17 00:00:00 2001
From: Xiaoyu Zhang <35585791+BBuf@users.noreply.github.com>
Date: Tue, 30 Dec 2025 23:39:32 +0800
Subject: [PATCH] [Diffusion] Zimage opt with qknorm and flashinfer rope
 (#16161)

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>
---
 .../runtime/models/dits/zimage.py             | 55 +++++++++++++------
 1 file changed, 38 insertions(+), 17 deletions(-)

diff --git a/python/sglang/multimodal_gen/runtime/models/dits/zimage.py b/python/sglang/multimodal_gen/runtime/models/dits/zimage.py
index f9743cebf..b14b63496 100644
--- a/python/sglang/multimodal_gen/runtime/models/dits/zimage.py
+++ b/python/sglang/multimodal_gen/runtime/models/dits/zimage.py
@@ -4,17 +4,21 @@ from typing import Any, List, Optional, Tuple
 import torch
 import torch.nn as nn
 
+from sglang.jit_kernel.norm import can_use_fused_inplace_qknorm
 from sglang.multimodal_gen.configs.models.dits.zimage import ZImageDitConfig
 from sglang.multimodal_gen.runtime.layers.activation import SiluAndMul
 from sglang.multimodal_gen.runtime.layers.attention import USPAttention
-from sglang.multimodal_gen.runtime.layers.layernorm import RMSNorm
+from sglang.multimodal_gen.runtime.layers.layernorm import RMSNorm, apply_qk_norm
 from sglang.multimodal_gen.runtime.layers.linear import (
     ColumnParallelLinear,
     MergedColumnParallelLinear,
     ReplicatedLinear,
     RowParallelLinear,
 )
-from sglang.multimodal_gen.runtime.layers.rotary_embedding import _apply_rotary_emb
+from sglang.multimodal_gen.runtime.layers.rotary_embedding import (
+    _apply_rotary_emb,
+    apply_flashinfer_rope_qk_inplace,
+)
 from sglang.multimodal_gen.runtime.models.dits.base import CachableDiT
 from sglang.multimodal_gen.runtime.platforms import current_platform
 from sglang.multimodal_gen.runtime.utils.layerwise_offload import OffloadableDiTMixin
@@ -151,23 +155,40 @@ class ZImageAttention(nn.Module):
         k = k.view(*k.shape[:-1], self.num_kv_heads, self.head_dim)
         v = v.view(*v.shape[:-1], self.num_kv_heads, self.head_dim)
 
-        if self.norm_q is not None:
-            q = self.norm_q(q)
-        if self.norm_k is not None:
-            k = self.norm_k(k)
-
-        # Apply RoPE
-        def apply_rotary_emb(
-            x_in: torch.Tensor,
-            freqs_cis: torch.Tensor,
-        ) -> Tuple[torch.Tensor, torch.Tensor]:
-            cos, sin = freqs_cis
-            x_out = _apply_rotary_emb(x_in, cos, sin, is_neox_style=False)
-            return x_out
+        if self.qk_norm:
+            if (
+                q.is_cuda
+                and (self.norm_q.variance_epsilon == self.norm_k.variance_epsilon)
+                and can_use_fused_inplace_qknorm(self.head_dim)
+            ):
+                q, k = apply_qk_norm(
+                    q=q,
+                    k=k,
+                    q_norm=self.norm_q,
+                    k_norm=self.norm_k,
+                    head_dim=self.head_dim,
+                    allow_inplace=True,
+                )
+            else:
+                q = self.norm_q(q)
+                k = self.norm_k(k)
 
         if freqs_cis is not None:
-            q = apply_rotary_emb(q, freqs_cis)
-            k = apply_rotary_emb(k, freqs_cis)
+            cos, sin = freqs_cis
+            if q.is_cuda and q.shape == k.shape:
+                cos_sin_cache = torch.cat(
+                    [
+                        cos.to(dtype=torch.float32).contiguous(),
+                        sin.to(dtype=torch.float32).contiguous(),
+                    ],
+                    dim=-1,
+                )
+                q, k = apply_flashinfer_rope_qk_inplace(
+                    q, k, cos_sin_cache, is_neox=False
+                )
+            else:
+                q = _apply_rotary_emb(q, cos, sin, is_neox_style=False)
+                k = _apply_rotary_emb(k, cos, sin, is_neox_style=False)
 
         hidden_states = self.attn(q, k, v)
         hidden_states = hidden_states.flatten(2)