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

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Message-ID: <20141003214124.GA31614@redhat.com>
Date:	Fri, 3 Oct 2014 23:41:24 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Chuck Ebbert <cebbert.lkml@...il.com>
Cc:	Sasha Levin <sasha.levin@...cle.com>, mingo@...nel.org,
	hpa@...or.com, linux-kernel@...r.kernel.org,
	torvalds@...ux-foundation.org, peterz@...radead.org,
	luto@...capital.net, dvlasenk@...hat.com, tglx@...utronix.de
Subject: Re: [tip:x86/asm] x86: Speed up ___preempt_schedule*() by using
	THUNK helpers

On 10/03, Chuck Ebbert wrote:
>
> > [  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
> > [  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
> > [  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
> > [  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
> > [  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
> > [  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
> > [  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
> > [  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
> > [  921.917752] ? ___preempt_schedule_context (arch/x86/lib/thunk_64.S:44)
> > [  921.917752] ? preempt_schedule_context (kernel/context_tracking.c:145)
>
> <snip lots of repeats of this>
>
> I *think* this is because RBP isn't being saved across task switch
> anymore?
>
> Without CONFIG_FRAME_POINTERS that night not be a problem...

Could you please spell?

I don't even understand "RBP isn't being saved", SAVE_CONTEXT/RESTORE_CONTEXT
do push/pop %rbp?

Thanks,

Oleg.

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