linux-kernel - Re: get_nohz_timer

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Date:	Fri, 8 Jul 2016 18:48:49 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Frederic Weisbecker <fweisbec@...il.com>
cc:	Richard Cochran <richardcochran@...il.com>,
	vatikaharlalka@...il.com,
	Preeti U Murthy <preeti@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>, stable@...r.kernel.org
Subject: Re: get_nohz_timer_target?

On Fri, 8 Jul 2016, Frederic Weisbecker wrote:
> On Fri, Jul 08, 2016 at 11:05:58AM +0200, Thomas Gleixner wrote:
> > On Mon, 18 Apr 2016, Richard Cochran wrote:
> > > Looking at kernel/sched/core.c:get_nohz_timer_target(), I don't
> > > understand the change made in:
> > > 
> > >     commit 9642d18eee2cd169b60c6ac0f20bda745b5a3d1e
> > >     Author: Vatika Harlalka <vatikaharlalka@...il.com>
> > >     Date:   Tue Sep 1 16:50:59 2015 +0200
> > >     nohz: Affine unpinned timers to housekeepers
> > > 
> > > After that change, the code now reads like this:
> > > 
> > > 	int i, cpu = smp_processor_id();
> > > 	struct sched_domain *sd;
> > > 
> > > 	if (!idle_cpu(cpu) && is_housekeeping_cpu(cpu))
> > > 		return cpu;
> > > 
> > > 	rcu_read_lock();
> > > 	for_each_domain(cpu, sd) {
> > > 		for_each_cpu(i, sched_domain_span(sd)) {
> > > 			if (!idle_cpu(i) && is_housekeeping_cpu(cpu)) {
> > > --------------------------------------------------------------- ^^^
> > > Was this supposed to be 'i' instead?
> > 
> > Yes. Care to send a patch?
> 
> Ah this got fixed already: 444969223c81c7d0a95136b7b4cfdcfbc96ac5bd
> ("sched/nohz: Fix affine unpinned timers mess")

Good. Though that patch misses a stable tag.

Thanks,

	tglx