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Re: [RFC] The Linux Scheduler: a Decade of Wasted Cores Report

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On Mon, 2016-04-25 at 11:34 +0200, Peter Zijlstra wrote:
> On Sat, Apr 23, 2016 at 06:38:25PM -0700, Brendan Gregg wrote:
> > 
> > Their proof of concept patches are online[1]. I tested them and saw
> > 0%
> > improvements on the systems I tested, for some simple workloads[2].
> > I
> > tested 1 and 2 node NUMA, as that is typical for my employer
> > (Netflix,
> > and our tens of thousands of Linux instances in the AWS/EC2 cloud),
> > even though I wasn't expecting any difference on 1 node. I've used
> > synthetic workloads so far.
> So their setup uses a bigger (not fully connected) NUMA topology, and
> I'm not entirely sure how much of their problems are due to that, but
> at
> least one of them is.
> 
> Such boxes are fairly rare.

Their proposed fix, of making sure we build all 8 sched
groups with 5 nodes each in them seems a little bit
roundabout when compared with a simpler alternative,
though.

When dealing with a NUMA_GLUELESS_MESH topology, we
should simply not build any sched domains with multiple
nodes inside them, except for the top level domain that
contains all the nodes.

At that point, we will balance between threads, inside
each core, and between all nodes, without running into
those pointless (and potentially harmful) intermediate
sched domains.

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[RFC] The Linux Scheduler: a Decade of Wasted Cores Report Jeff Merkey <linux.mdb@gmail.com> - 2016-04-23 20:30 +0200
  Re: [RFC] The Linux Scheduler: a Decade of Wasted Cores Report Brendan Gregg <brendan.d.gregg@gmail.com> - 2016-04-24 03:40 +0200
    Re: [RFC] The Linux Scheduler: a Decade of Wasted Cores Report Mike Galbraith <umgwanakikbuti@gmail.com> - 2016-04-24 09:10 +0200
      Re: [RFC] The Linux Scheduler: a Decade of Wasted Cores Report Mike Galbraith <umgwanakikbuti@gmail.com> - 2016-04-25 11:20 +0200
        [patch] sched: Fix smp nice induced group scheduling load  distribution woes Mike Galbraith <umgwanakikbuti@gmail.com> - 2016-04-27 09:20 +0200
          Re: [patch] sched: Fix smp nice induced group scheduling load  distribution woes Peter Zijlstra <peterz@infradead.org> - 2016-04-28 11:20 +0200
    Re: [RFC] The Linux Scheduler: a Decade of Wasted Cores Report Peter Zijlstra <peterz@infradead.org> - 2016-04-25 11:40 +0200
      Re: [RFC] The Linux Scheduler: a Decade of Wasted Cores Report Rik van Riel <riel@redhat.com> - 2016-04-25 20:00 +0200

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