linux-kernel - Re: [PATCH 10/19] sched/numa: Stop multiple tasks from moving to the cpu at the same time

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Message-ID: <1528135046.7898.111.camel@surriel.com>
Date:   Mon, 04 Jun 2018 13:57:26 -0400
From:   Rik van Riel <riel@...riel.com>
To:     Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
        Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 10/19] sched/numa: Stop multiple tasks from moving to
 the cpu at the same time

On Mon, 2018-06-04 at 15:30 +0530, Srikar Dronamraju wrote:
> Task migration under numa balancing can happen in parallel. More than
> one task might choose to migrate to the same cpu at the same time.
> This
> can result in
> - During task swap, choosing a task that was not part of the
> evaluation.
> - During task swap, task which just got moved into its preferred
> node,
>   moving to a completely different node.
> - During task swap, task failing to move to the preferred node, will
> have
>   to wait an extra interval for the next migrate opportunity.
> - During task movement, multiple task movements can cause load
> imbalance.
> 
> This problem is more likely if there are more cores per node or more
> nodes in the system.
> 
> Use a per run-queue variable to check if numa-balance is active on
> the
> run-queue.

> Signed-off-by: Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
> 

Reviewed-by: Rik van Riel <riel@...riel.com>
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