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From: Oleg Nesterov <oleg@redhat.com>
To: Chuck Ebbert <cebbert.lkml@gmail.com>
Cc: Sasha Levin <sasha.levin@oracle.com>,
	mingo@kernel.org, hpa@zytor.com, linux-kernel@vger.kernel.org,
	torvalds@linux-foundation.org, peterz@infradead.org,
	luto@amacapital.net, dvlasenk@redhat.com, tglx@linutronix.de
Subject: Re: [tip:x86/asm] x86: Speed up ___preempt_schedule*() by using THUNK helpers
Date: Sat, 4 Oct 2014 01:37:08 +0200	[thread overview]
Message-ID: <20141003233708.GA4019@redhat.com> (raw)
In-Reply-To: <20141003174814.6829cf26@as>

On 10/03, Chuck Ebbert wrote:
>
> On Fri, 3 Oct 2014 23:41:24 +0200
> Oleg Nesterov <oleg@redhat.com> wrote:
>
> > 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?
> >
>
> SAVE_ARGS/RESTORE_ARGS, which is what THUNK uses, doesn't push/pop %rbp
>
> Before, SAVE_ALL/RESTORE_ALL were being used around the call to
> preempt_schedule(). So from the symptoms I thought this was the problem.

Ah, thanks, now I understand what you meant. I thought you meant
switch_to().

Yes, I thought about this difference too, but so far I fail to understand
how this can make a difference, according to calling.h it is callee-saved.

Oleg.


  parent reply	other threads:[~2014-10-03 23:40 UTC|newest]

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-09-21 18:41 [PATCH v3 0/2] x86: reimplement ___preempt_schedule*() using THUNK helpers Oleg Nesterov
2014-09-21 18:41 ` [PATCH v3 1/2] " Oleg Nesterov
2014-09-24 15:02   ` [tip:x86/asm] x86: Speed up ___preempt_schedule*() by " tip-bot for Oleg Nesterov
2014-10-03  4:50     ` Sasha Levin
2014-10-03 13:39       ` Chuck Ebbert
2014-10-03 21:41         ` Oleg Nesterov
2014-10-03 21:56           ` Andy Lutomirski
2014-10-03 23:48             ` Linus Torvalds
2014-10-03 23:51             ` Oleg Nesterov
2014-10-03 22:48           ` Chuck Ebbert
2014-10-03 22:53             ` Andy Lutomirski
2014-10-03 23:13               ` H. Peter Anvin
2014-10-03 23:37             ` Oleg Nesterov [this message]
2014-10-03 21:16       ` Oleg Nesterov
2014-10-03 23:26       ` Oleg Nesterov
2014-10-04  0:01         ` Linus Torvalds
2014-10-04  0:11           ` Linus Torvalds
2014-10-04  0:33             ` Oleg Nesterov
2014-10-05 20:23               ` [PATCH 0/1] stop the unbound recursion in preempt_schedule_context() Oleg Nesterov
2014-10-05 20:23                 ` [PATCH 1/1] " Oleg Nesterov
2014-10-28 11:03                   ` [tip:sched/core] sched: " tip-bot for Oleg Nesterov
2014-10-05 23:53                 ` [PATCH 0/1] " Oleg Nesterov
2014-10-04  0:19           ` [tip:x86/asm] x86: Speed up ___preempt_schedule*() by using THUNK helpers Oleg Nesterov
2014-09-21 18:42 ` [PATCH v3 2/2] x86, lib/Makefile: remove the unnecessary "+= thunk_64.o" Oleg Nesterov
2014-09-24 15:02   ` [tip:x86/asm] x86/lib/Makefile: Remove " tip-bot for Oleg Nesterov

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