lkml.org 
[lkml]   [2013]   [Jun]   [28]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 7/8] sched: Split accounting of NUMA hinting faults that pass two-stage filter
On Fri, Jun 28, 2013 at 03:29:25PM +0100, Mel Gorman wrote:
> > Oh duh indeed. I totally missed it did that. Changelog also isn't giving
> > rationale for this. Mel?
> >
>
> There were a few reasons
>
> First, if there are many tasks sharing the page then they'll all move towards
> the same node. The node will be compute overloaded and then scheduled away
> later only to bounce back again. Alternatively the shared tasks would
> just bounce around nodes because the fault information is effectively
> noise. Either way I felt that accounting for shared faults with private
> faults would be slower overall.
>
> The second reason was based on a hypothetical workload that had a small
> number of very important, heavily accessed private pages but a large shared
> array. The shared array would dominate the number of faults and be selected
> as a preferred node even though it's the wrong decision.
>
> The third reason was because multiple threads in a process will race
> each other to fault the shared page making the information unreliable.
>
> It is important that *something* be done with shared faults but I haven't
> thought of what exactly yet. One possibility would be to give them a
> different weight, maybe based on the number of active NUMA nodes, but I had
> not tested anything yet. Peter suggested privately that if shared faults
> dominate the workload that the shared pages would be migrated based on an
> interleave policy which has some potential.
>

It would be good to put something like this in the Changelog, or even as
a comment near how we select the preferred node.


\
 
 \ /
  Last update: 2013-06-28 17:41    [W:0.101 / U:0.392 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site