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

From: Peter Zijlstra
Date: Fri Jul 18 2008 - 07:07:42 EST


On Fri, 2008-07-18 at 12:54 +0200, Ingo Molnar wrote:
> * Ingo Molnar <mingo@xxxxxxx> 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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