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* [glibc] x86: Don't set Prefer_No_AVX512 for processors with AVX512 and AVX-VNNI
@ 2021-12-06 15:14 H.J. Lu
  0 siblings, 0 replies; only message in thread
From: H.J. Lu @ 2021-12-06 15:14 UTC (permalink / raw)
  To: glibc-cvs

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=ceeffe968c01b1202e482f4855cb6baf5c6cb713

commit ceeffe968c01b1202e482f4855cb6baf5c6cb713
Author: H.J. Lu <hjl.tools@gmail.com>
Date:   Mon Dec 6 07:14:12 2021 -0800

    x86: Don't set Prefer_No_AVX512 for processors with AVX512 and AVX-VNNI
    
    Don't set Prefer_No_AVX512 on processors with AVX512 and AVX-VNNI since
    they won't lower CPU frequency when ZMM load and store instructions are
    used.

Diff:
---
 sysdeps/x86/cpu-features.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/sysdeps/x86/cpu-features.c b/sysdeps/x86/cpu-features.c
index be2498b2e7..311ade1f26 100644
--- a/sysdeps/x86/cpu-features.c
+++ b/sysdeps/x86/cpu-features.c
@@ -538,8 +538,11 @@ init_cpu_features (struct cpu_features *cpu_features)
 	  |= bit_arch_Prefer_No_VZEROUPPER;
       else
 	{
-	  cpu_features->preferred[index_arch_Prefer_No_AVX512]
-	    |= bit_arch_Prefer_No_AVX512;
+	  /* Processors with AVX512 and AVX-VNNI won't lower CPU frequency
+	     when ZMM load and store instructions are used.  */
+	  if (!CPU_FEATURES_CPU_P (cpu_features, AVX_VNNI))
+	    cpu_features->preferred[index_arch_Prefer_No_AVX512]
+	      |= bit_arch_Prefer_No_AVX512;
 
 	  /* Avoid RTM abort triggered by VZEROUPPER inside a
 	     transactionally executing RTM region.  */


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