linux-kernel - Re: [PATCH 4/4] sched/topology: the group balance cpu must be a cpu where the group is installed

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Date:   Tue, 25 Apr 2017 00:15:27 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Lauro Venancio <lvenanci@...hat.com>
Cc:     lwang@...hat.com, riel@...hat.com, Mike Galbraith <efault@....de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/4] sched/topology: the group balance cpu must be a cpu
 where the group is installed

On Mon, Apr 24, 2017 at 12:11:59PM -0300, Lauro Venancio wrote:
> On 04/24/2017 10:03 AM, Peter Zijlstra wrote:
> > On Thu, Apr 20, 2017 at 04:51:43PM -0300, Lauro Ramos Venancio wrote:
> >
> >> diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
> >> index e77c93a..694e799 100644
> >> --- a/kernel/sched/topology.c
> >> +++ b/kernel/sched/topology.c
> >> @@ -505,7 +507,11 @@ static void build_group_mask(struct sched_domain *sd, struct sched_group *sg)
> >>  
> >>  	for_each_cpu(i, sg_span) {
> >>  		sibling = *per_cpu_ptr(sdd->sd, i);
> >> -		if (!cpumask_test_cpu(i, sched_domain_span(sibling)))
> >> +
> >> +		if (!sibling->groups)
> >> +			continue;
> > How can this happen?
> This happens on machines with asymmetric topologies. For more details see:
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=c1174876874dcf8986806e4dad3d7d07af20b439

Ah, ok. I'll put a comment with.