Date: Mon, 27 Apr 2015 22:03:29 +0200
From: Borislav Petkov <bp@alien8.de>
To: "H. Peter Anvin" <hpa@zytor.com>
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>
Subject: Re: [PATCH] x86_64, asm: Work around AMD SYSRET SS descriptor
 attribute issue
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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.

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
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