linux-kernel - Re: [PATCH] sched: do not stop ticks when cpu is not idle

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Date:	Fri, 18 Jul 2008 18:29:05 +0200
From:	Heiko Carstens <heiko.carstens@...ibm.com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	eric miao <eric.y.miao@...il.com>, Ingo Molnar <mingo@...e.hu>,
	LKML <linux-kernel@...r.kernel.org>,
	Jack Ren <jack.ren@...vell.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Dmitry Adamushko <dmitry.adamushko@...il.com>
Subject: Re: [PATCH] sched: do not stop ticks when cpu is not idle

On Fri, Jul 18, 2008 at 05:27:28PM +0200, Thomas Gleixner wrote:
> On Fri, 18 Jul 2008, eric miao wrote:
> > On Fri, Jul 18, 2008 at 9:52 PM, Thomas Gleixner <tglx@...utronix.de> wrote:
> > >> Thomas, Peter, Dmitry, do you concur with the analysis? (commit below)
> > >
> > > Yes. I did not understand the issue when Jack pointed it out to me,
> > > but with Erics explanation it's really clear. Thanks for tracking that
> > > down.
> > 
> > Actually, Jack did most of the analysis and came up with this quick
> > fix.
> > 
> > >
> > >> It looks a bit ugly to me in the middle of schedule() - is there no wait
> > >> to solve this within kernel/time/*.c ?
> > >
> > > Hmm, yes. I think the proper fix is to enable the tick stop mechanism
> > > in the idle loop and disable it before we go to schedule. That takes
> > > an additional parameter to tick_nohz_stop_sched_tick(), but we then
> > > gain a very clear section where the nohz mimic can be active.
> > >
> > > I'll whip up a patch.
> > 
> > Sounds great, thanks.
> 
> Hey, thanks for tracking that down. I was banging my head against the
> wall when I understood the problem.
> 
> I tried to pinpoint the occasional softlockup bug reports, but I
> probably stared too long into that code so I just saw what I expected
> to see.
> 
> Can you give the patch below a try please ?

If this patch works, could you also add the s390 hunk before submitting?
Thanks! ;)
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