From 2f4a6addf3101342498b4528289c6fd053622530 Mon Sep 17 00:00:00 2001
From: Yibo Cai <yibo.cai@arm.com>
Date: Sun, 11 Jan 2026 20:27:19 +0800
Subject: [PATCH] [cpu/arm64] support run sglang on arm64 cpu (#14867)

---
 python/sglang/srt/layers/activation.py           | 12 ------------
 python/sglang/srt/layers/layernorm.py            |  9 ---------
 python/sglang/srt/layers/rotary_embedding.py     |  2 +-
 python/sglang/srt/model_executor/model_runner.py |  6 ++++--
 python/sglang/srt/utils/common.py                | 14 ++++++++++++--
 5 files changed, 17 insertions(+), 26 deletions(-)

diff --git a/python/sglang/srt/layers/activation.py b/python/sglang/srt/layers/activation.py
index 8fde6b80f..4b6f0f18d 100644
--- a/python/sglang/srt/layers/activation.py
+++ b/python/sglang/srt/layers/activation.py
@@ -378,15 +378,3 @@ def get_cross_encoder_activation_function(config: PretrainedConfig):
     else:
         # adapt bge-reranker
         return nn.Identity()
-
-
-if not (
-    _is_cuda or _is_npu or (_is_cpu and _is_cpu_amx_available) or _is_hip or _is_xpu
-):
-    logger.info(
-        "sgl-kernel is not available on Non-NV, Non-AMD platforms or Non-AMX CPUs. Fallback to other kernel libraries."
-    )
-    from vllm.model_executor.layers.activation import (  # noqa: F401
-        GeluAndMul,
-        SiluAndMul,
-    )
diff --git a/python/sglang/srt/layers/layernorm.py b/python/sglang/srt/layers/layernorm.py
index 7bef9d2ab..9f4c77a76 100644
--- a/python/sglang/srt/layers/layernorm.py
+++ b/python/sglang/srt/layers/layernorm.py
@@ -502,12 +502,3 @@ class Gemma3RMSNorm(MultiPlatformOp):
 
     def extra_repr(self):
         return f"{tuple(self.weight.shape)}, eps={self.eps}"
-
-
-if not (
-    _is_cuda or _is_hip or _is_npu or (_is_cpu and _is_cpu_amx_available) or _is_xpu
-):
-    logger.info(
-        "sgl-kernel layernorm implementation is not available on current platform. Fallback to other kernel libraries."
-    )
-    from vllm.model_executor.layers.layernorm import GemmaRMSNorm, RMSNorm  # noqa: F401
diff --git a/python/sglang/srt/layers/rotary_embedding.py b/python/sglang/srt/layers/rotary_embedding.py
index faa35d3c0..8fbdf3160 100644
--- a/python/sglang/srt/layers/rotary_embedding.py
+++ b/python/sglang/srt/layers/rotary_embedding.py
@@ -116,7 +116,7 @@ class RotaryEmbedding(MultiPlatformOp):
 
         if (
             (not (_is_cuda or _is_npu) or self.head_size not in [64, 128, 256, 512])
-            and not (_is_cpu and _is_cpu_amx_available)
+            and not (_is_cpu)
             and not (_is_xpu)
         ):
             if _is_cuda or _is_hip:
diff --git a/python/sglang/srt/model_executor/model_runner.py b/python/sglang/srt/model_executor/model_runner.py
index f3ce8cf4a..07e0cf7f5 100644
--- a/python/sglang/srt/model_executor/model_runner.py
+++ b/python/sglang/srt/model_executor/model_runner.py
@@ -148,6 +148,7 @@ from sglang.srt.utils import (
     get_local_ip_auto,
     init_custom_process_group,
     is_hip,
+    is_host_cpu_arm64,
     is_npu,
     log_info_on_rank0,
     monkey_patch_p2p_access_check,
@@ -178,6 +179,7 @@ from sglang.srt.weight_sync.tensor_bucket import (
 _is_hip = is_hip()
 _is_npu = is_npu()
 _is_cpu_amx_available = cpu_has_amx_support()
+_is_cpu_arm64 = is_host_cpu_arm64()
 
 if _is_npu:
     from sglang.srt.hardware_backend.npu.utils import init_npu_backend
@@ -729,7 +731,7 @@ class ModelRunner(ModelRunnerKVCacheMixin):
 
         if not self.is_draft_worker:
             if self.device == "cpu":
-                if _is_cpu_amx_available:
+                if _is_cpu_amx_available or _is_cpu_arm64:
                     # Bind OpenMP threads to CPU cores
                     torch.ops.sgl_kernel.init_cpu_threads_env(self.local_omp_cpuid)
 
@@ -743,7 +745,7 @@ class ModelRunner(ModelRunnerKVCacheMixin):
 
                 else:
                     logger.warning(
-                        "init_cpu_threads_env and shared memory based AllReduce is disabled since intel amx backend is not available"
+                        "init_cpu_threads_env and shared memory based AllReduce is disabled, only intel amx backend and arm64 are supported"
                     )
 
             # Only initialize the distributed environment on the target model worker.
diff --git a/python/sglang/srt/utils/common.py b/python/sglang/srt/utils/common.py
index 4b2110ed8..ad8217116 100644
--- a/python/sglang/srt/utils/common.py
+++ b/python/sglang/srt/utils/common.py
@@ -165,9 +165,19 @@ def is_host_cpu_x86() -> bool:
     )
 
 
+def is_host_cpu_arm64() -> bool:
+    machine = platform.machine().lower()
+    return (
+        machine in ("aarch64", "arm64")
+        and hasattr(torch, "cpu")
+        and torch.cpu.is_available()
+    )
+
+
 @lru_cache(maxsize=1)
 def is_cpu() -> bool:
-    return os.getenv("SGLANG_USE_CPU_ENGINE", "0") == "1" and is_host_cpu_x86()
+    is_host_cpu_supported = is_host_cpu_x86() or is_host_cpu_arm64()
+    return os.getenv("SGLANG_USE_CPU_ENGINE", "0") == "1" and is_host_cpu_supported
 
 
 def is_float4_e2m1fn_x2(dtype) -> bool:
@@ -3166,7 +3176,7 @@ def get_cpu_ids_by_node():
 
 def is_shm_available(dtype, world_size, local_size):
     return (
-        cpu_has_amx_support()
+        (cpu_has_amx_support() or is_host_cpu_arm64())
         and dtype in [torch.bfloat16, torch.float16, torch.float]
         and world_size >= 1
         and world_size == local_size