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Date: Fri, 3 Oct 2014 16:48:17 -0700
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Subject: Re: [tip:x86/asm] x86: Speed up ___preempt_schedule*() by using THUNK helpers
From: Linus Torvalds <torvalds@linux-foundation.org>
To: Andy Lutomirski <luto@amacapital.net>
Cc: Oleg Nesterov <oleg@redhat.com>, Chuck Ebbert <cebbert.lkml@gmail.com>,
        Sasha Levin <sasha.levin@oracle.com>, Ingo Molnar <mingo@kernel.org>,
        "H. Peter Anvin" <hpa@zytor.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Denys Vlasenko <dvlasenk@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>
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On Fri, Oct 3, 2014 at 2:56 PM, Andy Lutomirski <luto@amacapital.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