linux-kernel - Re: [patch v2 1/2] sched: Use resched IPI to kick off the nohz idle balance

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Date:	Tue, 04 Oct 2011 11:03:32 -0700
From:	Suresh Siddha <suresh.b.siddha@...el.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>,
	Venki Pallipadi <venki@...gle.com>,
	Ingo Molnar <mingo@...e.hu>,
	Prarit Bhargava <prarit@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"stable@...nel.org" <stable@...nel.org>
Subject: Re: [patch v2 1/2] sched: Use resched IPI to kick off the nohz idle
 balance

On Tue, 2011-10-04 at 02:05 -0700, Peter Zijlstra wrote:
> On Mon, 2011-10-03 at 15:09 -0700, Suresh Siddha wrote:
> > +               smp_mb();
> > +               /*
> > +                * Use smp_send_reschedule() instead of resched_cpu().
> > +                * This way we generate a sched IPI on the target cpu which
> > +                * is idle. And the softirq performing nohz idle load balance
> > +                * will be run before returning from the IPI.
> > +                */
> > +               smp_send_reschedule(ilb_cpu); 
> 
> Now the only thing missing is where the matching barrier is, does
> receiving an interrupt imply a mb? If so that wants mentioning
> somewhere, otherwise people will wonder how we can ever read the right
> value.

This is similar to resched_task()? Isn't it?

I am expecting the interrupt handlers will be already having the
necessary memory barriers, if the arch requires it.

thanks,
suresh


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