linux-kernel - Re: [PATCH v2] sched/core: Don't mix isolcpus and housekeeping CPUs

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Message-ID: <20181026084255.GZ3109@worktop.c.hoisthospitality.com>
Date:   Fri, 26 Oct 2018 10:42:55 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Cc:     Ingo Molnar <mingo@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Rik van Riel <riel@...riel.com>,
        Yi Wang <wang.yi59@....com.cn>, zhong.weidong@....com.cn,
        Yi Liu <liu.yi24@....com.cn>,
        Frederic Weisbecker <frederic@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v2] sched/core: Don't mix isolcpus and housekeeping CPUs

On Thu, Oct 25, 2018 at 11:53:17PM +0530, Srikar Dronamraju wrote:
> > 
> > You can create multiple partitions with cpusets but still have an
> > unbound task in the root cgroup. That would suffer the exact same
> > problems.
> > 
> 
> I probably don't understand this. Even if the child cgroups has
> cpu_exclusive or sched_load_balance reset, the tasks in root cgroup has
> access to all cpus in system. Right?

The crucial word being 'access'. The root group will not impose a limit
on the affinity of tasks. So you can indeed have affinities that span
load balancing domains.

And yes, that leads to 'interesting' but specified behaviour.