Messages in this thread | | | Date | Fri, 25 Apr 2014 10:09:59 +0100 | From | Mel Gorman <> | Subject | Re: [PATCH 3/3] sched,numa: do not set preferred_node on migration to a second choice node |
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On Fri, Apr 11, 2014 at 01:00:29PM -0400, riel@redhat.com wrote: > From: Rik van Riel <riel@redhat.com> > > Setting the numa_preferred_node for a task in task_numa_migrate > does nothing on a 2-node system. Either we migrate to the node > that already was our preferred node, or we stay where we were. > > On a 4-node system, it can slightly decrease overhead, by not > calling the NUMA code as much. Since every node tends to be > directly connected to every other node, running on the wrong > node for a while does not do much damage. >
Guess what size of machine I do the vast bulk of testing of automatic NUMA balancing on!
> However, on an 8 node system, there are far more bad nodes > than there are good ones, and pretending that a second choice > is actually the preferred node can greatly delay, or even > prevent, a workload from converging. > > The only time we can safely pretend that a second choice > node is the preferred node is when the task is part of a > workload that spans multiple NUMA nodes. > > Signed-off-by: Rik van Riel <riel@redhat.com> > Tested-by: Vinod Chegu <chegu_vinod@hp.com>
Acked-by: Mel Gorman <mgorman@suse.de>
-- Mel Gorman SUSE Labs
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