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

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Message-Id: <20181024103002.GB18466@linux.vnet.ibm.com>
Date:   Wed, 24 Oct 2018 16:00:02 +0530
From:   Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
To:     Peter Zijlstra <peterz@...radead.org>
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

* Peter Zijlstra <peterz@...radead.org> [2018-10-24 12:03:23]:

> It appears to me the for_each_online_node() iteration in
> task_numa_migrate() needs an addition test to see if the selected node
> has any CPUs in the relevant sched_domain _at_all_.
> 

Yes, this should work.
Yi Wang does this extra check a little differently.

http://lkml.kernel.org/r/1540177516-38613-1-git-send-email-wang.yi59@zte.com.cn

However the last time I had posted you didn't like that approach.
http://lkml.kernel.org/r/20170406073659.y6ubqriyshax4v4m@hirez.programming.kicks-ass.net

Further, I would think the number of times, we would be calling
sched_setaffinity would be far less than task_numa_migrate().
In the regular case, where we never have isolcpus, we add this extra check.

Also what does it mean for a task to have its cpu affinity set to a mix of
isolcpus and non isolcpus.

Also should we be updating update_numa_stats accordingly? While the problem
may not be apparent there but we are counting the load and compute capacity
of isolcpus.

-- 
Thanks and Regards
Srikar Dronamraju