linux-kernel - Re: [patch 1/2] idle profile hits with NOHZ

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Date:	Fri, 29 May 2009 15:15:26 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Martin Schwidefsky <schwidefsky@...ibm.com>
cc:	linux-kernel@...r.kernel.org, Rob van der Heij <rvdheij@...il.com>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	Ingo Molnar <mingo@...e.hu>, john stultz <johnstul@...ibm.com>
Subject: Re: [patch 1/2] idle profile hits with NOHZ

On Fri, 29 May 2009, Martin Schwidefsky wrote:
> On Thu, 28 May 2009 22:19:44 +0200 (CEST)
> Thomas Gleixner <tglx@...utronix.de> wrote:
> 
> > On Thu, 28 May 2009, Martin Schwidefsky wrote:
> > > --- quilt-2.6.orig/kernel/time/tick-sched.c
> > > +++ quilt-2.6/kernel/time/tick-sched.c
> > > @@ -166,6 +166,7 @@ static void tick_nohz_stop_idle(int cpu)
> > >  		ts->idle_lastupdate = now;
> > >  		ts->idle_sleeptime = ktime_add(ts->idle_sleeptime, delta);
> > >  		ts->idle_active = 0;
> > > +		ts->idle_pc = profile_pc(get_irq_regs());
> > 
> >   Hmm, tick_nohz_stop_idle() is called from
> >   tick_nohz_restart_sched_tick() as well in the context of the idle
> >   task.
> > 
> >   I think there is no guarantee that get_irq_regs() will return
> >   anything useful in thread context.
> > 
> >   So get_irq_regs() might return a NULL pointer which will explode
> >   some of the profile_pc() implementations. If not it can still feed
> >   total nonsense to the profile_hits() call.
> 
> Drat, but if it is called from idle we should be able to just skip the
> assignment to ts->idle_pc, no? Then a simple in_interrupt() test is
> missing.

That should do the trick.

Thanks,

	tglx
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