linux-kernel - Re: [tip:x86/asm] x86: Speed up ___preempt

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Message-ID: <CA+55aFx7n9nsfMYELGN0Kev13pHUgzMBtPyovyBf8-LUYTC9bg@mail.gmail.com>
Date:	Fri, 3 Oct 2014 16:48:17 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Oleg Nesterov <oleg@...hat.com>,
	Chuck Ebbert <cebbert.lkml@...il.com>,
	Sasha Levin <sasha.levin@...cle.com>,
	Ingo Molnar <mingo@...nel.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [tip:x86/asm] x86: Speed up ___preempt_schedule*() by using THUNK helpers

On Fri, Oct 3, 2014 at 2:56 PM, Andy Lutomirski <luto@...capital.net> wrote:
>
> Is this thing missing a flags or cc clobber:
>
> # define __preempt_schedule() asm ("call ___preempt_schedule")

Yes, it should probably have a cc clobber. Although I think thet gcc
actually assumes all asms clobber flags on x86, so it shouldn't
matter.

> Is this all just to make the call sequence for preempt_schedule shorter?

Not so much the call sequence, but the code around the call - not
havign to spill live registers etc. But yes.

              Linus
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