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

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Date:	Fri, 18 Jul 2008 13:08:03 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	eric miao <eric.y.miao@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Jack Ren <jack.ren@...vell.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Dmitry Adamushko <dmitry.adamushko@...il.com>
Subject: Re: [PATCH] sched: do not stop ticks when cpu is not idle

On Fri, 2008-07-18 at 12:54 +0200, Ingo Molnar wrote:
> * Ingo Molnar <mingo@...e.hu> wrote:
> 
> > --- a/kernel/sched.c
> > +++ b/kernel/sched.c
> > @@ -4446,7 +4446,8 @@ need_resched_nonpreemptible:
> >  		rq->nr_switches++;
> >  		rq->curr = next;
> >  		++*switch_count;
> > -
> > +		if (rq->curr != rq->idle)
> > +			tick_nohz_restart_sched_tick();
> >  		context_switch(rq, prev, next); /* unlocks the rq */
> 
> hm, one problem i can see is lock dependencies. This code is executed 
> with the rq lock while tick_nohz_restart_sched_tick() takes hr locks => 
> not good. So i havent applied this just yet - this needs to be solved 
> differently.

Actually, that should work these days...

Also, I assume Eric actually tested this with lockdep enabled (right,
Eric?) and that'll shout - or rather, lockup hard in this case - if you
got it wrong.

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