From: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
To: Mel Gorman <mgorman@techsingularity.net>
Cc: Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@kernel.org>, Rik van Riel <riel@surriel.com>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 3/4] sched/numa: Stop comparing tasks for NUMA placement after selecting an idle core
Date: Fri, 7 Sep 2018 18:35:53 +0530 [thread overview]
Message-ID: <20180907130553.GB3995@linux.vnet.ibm.com> (raw)
In-Reply-To: <20180907101139.20760-4-mgorman@techsingularity.net>
* Mel Gorman <mgorman@techsingularity.net> [2018-09-07 11:11:38]:
> task_numa_migrate is responsible for finding a core on a preferred NUMA
> node for a task. As part of this, task_numa_find_cpu iterates through
> the CPUs of a node and evaulates CPUs, both idle and with running tasks,
> as placement candidates. Generally though, any idle CPU is equivalent in
> terms of improving imbalances and a search after finding one is pointless.
> This patch stops examining CPUs on a node if an idle CPU is considered
> suitable.
>
However there can be a thread on the destination node that might benefit
from swapping with the current thread. Don't we loose that opportunity to
swap if skip checking for other threads?
To articulate.
Thread A currently running on node 0 wants to move to node 1.
Thread B currently running on node 1 is better of if it ran on node 0.
Thread A seems idle cpu before seeing Thread B; skips and looses
an opportunity to swap.
Eventually thread B will get an opportunity to move to node 0, when thread B
calls task_numa_placement but we are probably stopping it from achieving
earlier.
--
Thanks and Regards
Srikar Dronamraju
next prev parent reply other threads:[~2018-09-07 13:06 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-09-07 10:11 [PATCH 0/4] Follow-up fixes for v4.19-rc1 NUMA balancing Mel Gorman
2018-09-07 10:11 ` [PATCH 1/4] sched/numa: Remove redundant numa_stats nr_running field Mel Gorman
2018-09-07 10:11 ` [PATCH 2/4] sched/numa: Remove unused calculations in update_numa_stats Mel Gorman
2018-09-07 10:11 ` [PATCH 3/4] sched/numa: Stop comparing tasks for NUMA placement after selecting an idle core Mel Gorman
2018-09-07 13:05 ` Srikar Dronamraju [this message]
2018-09-07 14:20 ` Mel Gorman
2018-09-07 10:11 ` [PATCH 4/4] sched/numa: Do not move imbalanced load purely on the basis of an idle CPU Mel Gorman
2018-09-07 11:33 ` Peter Zijlstra
2018-09-07 12:37 ` Mel Gorman
2018-09-07 12:44 ` Peter Zijlstra
2018-09-07 13:42 ` Srikar Dronamraju
2018-09-07 14:28 ` Mel Gorman
2018-09-10 9:41 ` Mel Gorman
2018-09-12 6:54 ` Srikar Dronamraju
2018-09-12 9:36 ` Peter Zijlstra
2018-09-12 10:45 ` Srikar Dronamraju
2018-09-12 9:57 ` Ingo Molnar
2018-09-12 10:27 ` Srikar Dronamraju
2018-09-12 10:57 ` Mel Gorman
2018-09-12 10:52 ` Mel Gorman
2018-09-07 11:24 ` [PATCH 0/4] Follow-up fixes for v4.19-rc1 NUMA balancing Peter Zijlstra
2018-09-07 12:29 ` Mel Gorman
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