linux-kernel - Re: [RFC 3/3] sched/topology: Different sched groups must not have the same balance cpu

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Date:   Fri, 14 Apr 2017 18:49:09 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Lauro Ramos Venancio <lvenanci@...hat.com>
Cc:     linux-kernel@...r.kernel.org, lwang@...hat.com, riel@...hat.com,
        Mike Galbraith <efault@....de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>
Subject: Re: [RFC 3/3] sched/topology: Different sched groups must not have
 the same balance cpu

On Thu, Apr 13, 2017 at 10:56:09AM -0300, Lauro Ramos Venancio wrote:
> Currently, the group balance cpu is the groups's first CPU. But with
> overlapping groups, two different groups can have the same first CPU.
> 
> This patch uses the group mask to mark all the CPUs that have a
> particular group as its main sched group. The group balance cpu is the
> first group CPU that is also in the mask.

Please give a NUMA configuration and CPU number where this goes wrong.

Because only the first group of a domain matters, and with the other
thing fixed, I'm not immediately seeing where we go wobbly.