From: litenglong <litenglong@kylinos.cn>
Date: Fri, 17 Oct 2025 01:45:41 +0000 (+0800)
Subject: x86: Disable AVX Fast Unaligned Load on Hygon 1/2/3
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=00d406e77bb0e49d79dc1b13d7077436ee5cdf14;p=thirdparty%2Fglibc.git

x86: Disable AVX Fast Unaligned Load on Hygon 1/2/3

- Performance testing revealed significant memcpy performance degradation
  when bit_arch_AVX_Fast_Unaligned_Load is enabled on Hygon 3.
- Hygon confirmed AVX performance issues in certain memory functions.
- Glibc benchmarks show SSE outperforms AVX for
  memcpy/memmove/memset/strcmp/strcpy/strlen and so on.
- Hardware differences primarily in floating-point operations don't justify
  AVX usage for memory operations.

Reviewed-by: gaoxiang <gaoxiang@kylinos.cn>
Signed-off-by: litenglong <litenglong@kylinos.cn>
Reviewed-by: H.J. Lu <hjl.tools@gmail.com>
---

diff --git a/sysdeps/x86/cpu-features.c b/sysdeps/x86/cpu-features.c
index b67ef541dd..c696a4d1f7 100644
--- a/sysdeps/x86/cpu-features.c
+++ b/sysdeps/x86/cpu-features.c
@@ -1123,6 +1123,12 @@ disable_tsx:
        hardware.  */
       cpu_features->preferred[index_arch_Avoid_Non_Temporal_Memset]
 	    &= ~bit_arch_Avoid_Non_Temporal_Memset;
+      if (model < 0x4)
+	{
+	  /*  Unaligned AVX loads are slower.  */
+	  cpu_features->preferred[index_arch_AVX_Fast_Unaligned_Load]
+	    &= ~bit_arch_AVX_Fast_Unaligned_Load;
+	}
     }
   else
     {