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Subject: Re: [PATCH] x86_64, asm: Work around AMD SYSRET SS descriptor attribute issue
From: "H. Peter Anvin" <hpa@zytor.com>
Date: Mon, 27 Apr 2015 13:14:51 -0700
To: Borislav Petkov <bp@alien8.de>
CC: Linus Torvalds <torvalds@linux-foundation.org>,
        Andy Lutomirski <luto@amacapital.net>,
        Andy Lutomirski <luto@kernel.org>, X86 ML <x86@kernel.org>,
        Denys Vlasenko <vda.linux@googlemail.com>,
        Brian Gerst <brgerst@gmail.com>, Denys Vlasenko <dvlasenk@redhat.com>,
        Ingo Molnar <mingo@kernel.org>, Steven Rostedt <rostedt@goodmis.org>,
        Oleg Nesterov <oleg@redhat.com>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Alexei Starovoitov <ast@plumgrid.com>, Will Drewry <wad@chromium.org>,
        Kees Cook <keescook@chromium.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Message-ID: <2F6CA156-F03F-4F49-A6B9-7D1D1E1D805B@zytor.com>
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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.

-- 
Sent from my mobile phone.  Please pardon brevity and lack of formatting.
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