linux-kernel - Re: cond_resched() and RCU CPU stall warnings

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Message-ID: <1394950455.5470.16.camel@marge.simpson.net>
Date:	Sun, 16 Mar 2014 07:14:15 +0100
From:	Mike Galbraith <umgwanakikbuti@...il.com>
To:	paulmck@...ux.vnet.ibm.com
Cc:	peterz@...radead.org, mingo@...e.hu, josh@...htriplett.org,
	laijs@...fujitsu.com, linux-kernel@...r.kernel.org
Subject: Re: cond_resched() and RCU CPU stall warnings

On Sun, 2014-03-16 at 07:09 +0100, Mike Galbraith wrote: 
> On Sat, 2014-03-15 at 18:59 -0700, Paul E. McKenney wrote: 

> > diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> > index b46131ef6aab..994d2b0fd0b2 100644
> > --- a/kernel/sched/core.c
> > +++ b/kernel/sched/core.c
> > @@ -4075,6 +4075,9 @@ int __sched _cond_resched(void)
> >  		__cond_resched();
> >  		return 1;
> >  	}
> > +	preempt_disable();
> > +	rcu_note_context_switch(smp_processor_id());
> > +	preempt_enable();
> >  	return 0;
> >  }
> >  EXPORT_SYMBOL(_cond_resched);
> 
> Hm.  Since you only care about the case where your task is solo, how
> about do racy checks, 100% accuracy isn't required is it?  Seems you
> wouldn't want to unconditionally do that in tight loops.

(or do that in scheduler_tick()?)

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