| Date | Tue, 5 Jun 2018 10:51:38 +0100 | From | Mel Gorman <> | Subject | Re: [PATCH 10/19] sched/numa: Stop multiple tasks from moving to the cpu at the same time |
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On Mon, Jun 04, 2018 at 03:30:19PM +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. >
FWIW, I had noticed a similar problem when selecting an idle CPU for SIS. When prototying something to look at nearby CPUs for cross-node migrations during wake_affine I found that the patch allowed multiple tasks to select the same CPU when a waker was waking many wakees and ultimately dropped the patch.
Either way for this patch;
Acked-by: Mel Gorman <mgorman@techsingularity.net>
-- Mel Gorman SUSE Labs
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