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crypto/x86_64cpuid.pl: suppress AVX512F flag on Skylake-X.

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It was observed that AVX512 code paths can negatively affect overall
Skylake-X system performance. But we are talking specifically about
512-bit code, while AVX512VL, 256-bit variant of AVX512F instructions,
is supposed to fly as smooth as AVX2. Which is why it remains unmasked.

Reviewed-by: Rich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/4838)
This commit is contained in:
Andy Polyakov 2017-12-04 14:03:05 +01:00
parent 05de3a5be9
commit 7933762870
1 changed files with 8 additions and 0 deletions
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8
crypto/x86_64cpuid.pl
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@ -139,6 +139,7 @@ OPENSSL_ia32_cpuid:
.Lnocacheinfo:
mov \$1,%eax
cpuid
movd %eax,%xmm0 # put aside processor id
and \$0xbfefffff,%edx # force reserved bits to 0
cmp \$0,%r9d
jne .Lnotintel
@ -186,6 +187,13 @@ OPENSSL_ia32_cpuid:
jc .Lnotknights
and \$0xfff7ffff,%ebx # clear ADCX/ADOX flag
.Lnotknights:
movd %xmm0,%eax # restore processor id
and \$0x0fff0ff0,%eax
cmp \$0x00050650,%eax # Skylake-X
jne .Lnotskylakex
and \$0xfffeffff,%ebx # ~(1<<16)
# suppress AVX512F flag on Skylake-X
.Lnotskylakex:
mov %ebx,8(%rdi) # save extended feature flags
mov %ecx,12(%rdi)
.Lno_extended_info: