From a3d9a218826a1b70e66e8c7908f22d0c3e488044 Mon Sep 17 00:00:00 2001
From: Xiaoyu Zhang <35585791+BBuf@users.noreply.github.com>
Date: Mon, 19 Jan 2026 15:24:11 +0800
Subject: [PATCH] Revert "[Perf] fuse q, k norm for Flux2Attention (#17241)"
 (#17332)

---
 .../multimodal_gen/runtime/layers/layernorm.py     | 14 +++-----------
 .../multimodal_gen/runtime/models/dits/flux_2.py   |  8 +++++---
 2 files changed, 8 insertions(+), 14 deletions(-)

diff --git a/python/sglang/multimodal_gen/runtime/layers/layernorm.py b/python/sglang/multimodal_gen/runtime/layers/layernorm.py
index 4bd9368ee..a9f5811e2 100644
--- a/python/sglang/multimodal_gen/runtime/layers/layernorm.py
+++ b/python/sglang/multimodal_gen/runtime/layers/layernorm.py
@@ -443,15 +443,6 @@ def apply_qk_norm(
     """
 
     batch_size = q.size(0)
-    q_shape = q.shape
-    k_shape = k.shape
-
-    # Ensure contiguous for view operation
-    if not q.is_contiguous():
-        q = q.contiguous()
-    if not k.is_contiguous():
-        k = k.contiguous()
-
     q_eps = q_norm.variance_epsilon
     k_eps = k_norm.variance_epsilon
     # Only try fused path on CUDA and when it won't introduce implicit copies.
@@ -469,8 +460,7 @@ def apply_qk_norm(
             head_dim=head_dim,
             eps=q_eps,
         )
-        # Inplace kernel modifies q, k - return with original shape
-        return q.view(q_shape), k.view(k_shape)
+        return q, k
 
     # Fallback for AMD/ROCm: apply RMSNorm separately to q and k
     import warnings
@@ -479,6 +469,8 @@ def apply_qk_norm(
         "Fused QK-norm not available, using RMSNorm fallback",
         stacklevel=2,
     )
+    q_shape = q.shape
+    k_shape = k.shape
     q_out = q_norm(q.view(-1, head_dim)).view(q_shape)
     k_out = k_norm(k.view(-1, head_dim)).view(k_shape)
     return q_out, k_out
diff --git a/python/sglang/multimodal_gen/runtime/models/dits/flux_2.py b/python/sglang/multimodal_gen/runtime/models/dits/flux_2.py
index 585c30cb5..a157b88d3 100644
--- a/python/sglang/multimodal_gen/runtime/models/dits/flux_2.py
+++ b/python/sglang/multimodal_gen/runtime/models/dits/flux_2.py
@@ -22,7 +22,7 @@ from diffusers.models.normalization import AdaLayerNormContinuous
 
 from sglang.multimodal_gen.configs.models.dits.flux import FluxConfig
 from sglang.multimodal_gen.runtime.layers.attention import USPAttention
-from sglang.multimodal_gen.runtime.layers.layernorm import RMSNorm, apply_qk_norm
+from sglang.multimodal_gen.runtime.layers.layernorm import RMSNorm
 from sglang.multimodal_gen.runtime.layers.linear import ColumnParallelLinear
 from sglang.multimodal_gen.runtime.layers.rotary_embedding import (
     NDRotaryEmbedding,
@@ -196,7 +196,8 @@ class Flux2Attention(torch.nn.Module, AttentionModuleMixin):
         key = key.unflatten(-1, (self.heads, -1))
         value = value.unflatten(-1, (self.heads, -1))
 
-        query, key = apply_qk_norm(query, key, self.norm_q, self.norm_k, self.head_dim)
+        query = self.norm_q(query)
+        key = self.norm_k(key)
 
         if self.added_kv_proj_dim is not None:
             encoder_query = encoder_query.unflatten(-1, (self.heads, -1))
@@ -339,7 +340,8 @@ class Flux2ParallelSelfAttention(torch.nn.Module, AttentionModuleMixin):
         key = key.unflatten(-1, (self.heads, -1))
         value = value.unflatten(-1, (self.heads, -1))
 
-        query, key = apply_qk_norm(query, key, self.norm_q, self.norm_k, self.head_dim)
+        query = self.norm_q(query)
+        key = self.norm_k(key)
 
         if freqs_cis is not None:
             cos, sin = freqs_cis