linux-kernel - Re: [PATCH v2 00/19] Fixes for sched/numa

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Message-Id: <20180723150954.GI30345@linux.vnet.ibm.com>
Date:   Mon, 23 Jul 2018 08:09:55 -0700
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>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v2 00/19]  Fixes for sched/numa_balancing

* Peter Zijlstra <peterz@...radead.org> [2018-07-23 15:57:00]:

> On Wed, Jun 20, 2018 at 10:32:41PM +0530, Srikar Dronamraju wrote:
> > Srikar Dronamraju (19):
> >   sched/numa: Remove redundant field.
> >   sched/numa: Evaluate move once per node
> >   sched/numa: Simplify load_too_imbalanced
> >   sched/numa: Set preferred_node based on best_cpu
> >   sched/numa: Use task faults only if numa_group is not yet setup
> >   sched/debug: Reverse the order of printing faults
> >   sched/numa: Skip nodes that are at hoplimit
> >   sched/numa: Remove unused task_capacity from numa_stats
> >   sched/numa: Modify migrate_swap to accept additional params
> >   sched/numa: Restrict migrating in parallel to the same node.
> >   sched/numa: Remove numa_has_capacity
> >   sched/numa: Use group_weights to identify if migration degrades locality
> >   sched/numa: Move task_placement closer to numa_migrate_preferred
>
> I took the above, but left the below for next time.


>
> >   sched/numa: Stop multiple tasks from moving to the cpu at the same time

This patch has go-ahead from Mel and Rik and no outstanding comments.

In my analysis, I did find a lot of cases where the same cpu ended up
being the target. + I am not sure you can apply "sched/numa: Restrict
migrating in parallel to the same node" cleanly without this patch.

So I am a bit confused. If possible, please clarify.

> >   mm/migrate: Use xchg instead of spinlock

Will try with spin_trylock and get back.

> >   sched/numa: Updation of scan period need not be in lock

I didnt see any comments for this apart from an ack from Rik.
+ It thought it was trivial and shouldnt have any side-effect.

> >   sched/numa: Detect if node actively handling migration
> >   sched/numa: Pass destination cpu as a parameter to migrate_task_rq
> >   sched/numa: Reset scan rate whenever task moves across nodes
>