linux-kernel - Re: [PATCH v2 32/36] x86/entry: Micro-optimize compat fast syscall arg fetch

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Message-ID: <CALCETrUmNtXZQZQEe=pxqX0bGS2sf15YXfChNMLigmZgzytc+w@mail.gmail.com>
Date:	Fri, 9 Oct 2015 12:28:46 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Andy Lutomirski <luto@...nel.org>, X86 ML <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Brian Gerst <brgerst@...il.com>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Borislav Petkov <bp@...en8.de>
Subject: Re: [PATCH v2 32/36] x86/entry: Micro-optimize compat fast syscall
 arg fetch

On Fri, Oct 9, 2015 at 12:32 AM, Ingo Molnar <mingo@...nel.org> wrote:
>
> * Andy Lutomirski <luto@...nel.org> wrote:
>
>> we're following a 32-bit pointer, and the uaccess code isn't smart
>> enough to figure out that the access_ok check isn't needed.
>>
>> This saves about three cycles on a cache-hot fast syscall.
>
> Another request: could you please stick the benchmarking code of the various x86
> system call variants into 'perf bench' - under tools/perf/bench/, so that
> measurements can be done on more hardware and can be reproduced easily?
>
> I'd suggest we dedicate an entirely new benchmark family to it: 'perf bench x86'
> and then have:
>
>    perf bench x86 syscall vdso
>    perf bench x86 syscall int80
>    perf bench x86 syscall vdso-compat

I'll play with this.  I'm not too familiar with the perf bench stuff.

--Andy
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