linux-kernel - Re: [PATCH 11/19] sched/numa: Restrict migrating in parallel to the same node.

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Message-ID: <1528135170.7898.113.camel@surriel.com>
Date:   Mon, 04 Jun 2018 13:59:30 -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 11/19] sched/numa: Restrict migrating in parallel to the
 same node.

On Mon, 2018-06-04 at 15:30 +0530, Srikar Dronamraju wrote:
> Since task migration under numa balancing can happen in parallel,
> more
> than one task might choose to move to the same node at the same time.
> This can cause load imbalances at the node level.
> 
> The problem is more likely if there are more cores per node or more
> nodes in system.
> 
> Use a per-node variable to indicate if task migration
> to the node under numa balance is currently active.
> This per-node variable will not track swapping of tasks.

> The commit does cause some performance regression but is needed from
> a fairness/correctness perspective.

Does it help any "real workloads", even simple things
like SpecJBB2005?

If this patch only causes regressions, and does not help
any workloads, I would argue that it is not in fact needed.

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