Re: [PATCH] x86_64, asm: Work around AMD SYSRET SS descriptor attribute issue

H. Peter Anvin
2015-04-27T20:15:32Z

I did a microbenchmark in user space... let's see if I can find it.

On April 27, 2015 1:03:29 PM PDT, Borislav Petkov <bp@alien8.de> wrote:
>On Mon, Apr 27, 2015 at 12:59:11PM -0700, H. Peter Anvin wrote:
>> It really comes down to this: it seems older cores from both Intel
>> and AMD perform better with 66 66 66 90, whereas the 0F 1F series is
>> better on newer cores.
>>
>> When I measured it, the differences were sometimes dramatic.
>
>How did you measure that? I should probably do the same on some newer
>AMD machines... We're using k8_nops on all AMD, even though the
>optimization manuals cite different NOPs on newer AMD families.
>
>Thanks.

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