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Date: Sat, 4 Oct 2014 01:51:45 +0200 From: Oleg Nesterov <oleg@...hat.com> To: Andy Lutomirski <luto@...capital.net> Cc: 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>, Linus Torvalds <torvalds@...ux-foundation.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 10/03, Andy Lutomirski wrote: > > Is this thing missing a flags or cc clobber: > > # define __preempt_schedule() asm ("call ___preempt_schedule") Well, calling.h says "rflags is clobbered", so probably yes? > Also, I'm at a loss as to wtf all this code is doing. > > There's preempt_schedule, which appears to be a normal C function. > > There's ___preempt_schedule, which is written in assembly and calls > preempt_schedule. > > Then there's __preempt_schedule, which is an inline assembler function > that calls ___preempt_schedule. > > Is this all just to make the call sequence for preempt_schedule shorter? Yes, please look at 1a338ac32ca630f67df25b4a16436cccc314e997 sched, x86: Optimize the preempt_schedule() call Remove the bloat of the C calling convention out of the preempt_enable() sites by creating an ASM wrapper which allows us to do an asm("call ___preempt_schedule") instead. Oleg. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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