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    SubjectRe: [PATCH v2 0/8] sched/fair: rework the CFS load balance
    Hi Phil,

    On Thu, 29 Aug 2019 at 21:23, Phil Auld <pauld@redhat.com> wrote:
    >
    > On Thu, Aug 01, 2019 at 04:40:16PM +0200 Vincent Guittot wrote:
    > > Several wrong task placement have been raised with the current load

    > >
    > > --
    > > 2.7.4
    > >
    >
    > I keep expecting a v3 so I have not dug into all the patches in detail. However, I've

    v3 is under preparation

    > been working with them from Vincent's tree while they were under development so I thought
    > I'd add some results.

    Yes. thanks for your help.

    >
    > The workload is a test our perf team came up with to illustrate the issues we were seeing
    > with imbalance in the presence of group scheduling.
    >
    > On a 4-numa X 20 cpu system (smt on) we run a 76 thread lu.C benchmark from the NAS Parallel
    > suite. And at the same time run 2 stress cpu burn processes. The GROUP test puts the
    > benchmark and the stress processes each in its own cgroup. The NORMAL case puts them all
    > in the first cgroup. The results show first the average number of threads of each type
    > running on each of the numa nodes based on sampling taken during the run. This is followed
    > by the lu.C benchmark results. There are 3 runs of GROUP and 2 runs of NORMAL shown.
    >
    > Before (linux-5.3-rc1+ @ a1dc0446d649)
    >
    > lu.C.x_76_GROUP_1.stress.ps.numa.hist Average 0.00 1.00 1.00
    > lu.C.x_76_GROUP_2.stress.ps.numa.hist Average 0.00 1.00 1.00
    > lu.C.x_76_GROUP_3.stress.ps.numa.hist Average 0.00 1.00 1.00
    > lu.C.x_76_NORMAL_1.stress.ps.numa.hist Average 1.15 0.23 0.00 0.62
    > lu.C.x_76_NORMAL_2.stress.ps.numa.hist Average 1.67 0.00 0.00 0.33
    >
    > lu.C.x_76_GROUP_1.ps.numa.hist Average 30.45 6.95 4.52 34.08
    > lu.C.x_76_GROUP_2.ps.numa.hist Average 32.33 8.94 9.21 25.52
    > lu.C.x_76_GROUP_3.ps.numa.hist Average 30.45 8.91 12.09 24.55
    > lu.C.x_76_NORMAL_1.ps.numa.hist Average 18.54 19.23 19.69 18.54
    > lu.C.x_76_NORMAL_2.ps.numa.hist Average 17.25 19.83 20.00 18.92
    >
    > ============76_GROUP========Mop/s===================================
    > min q1 median q3 max
    > 2119.92 2418.1 2716.28 3147.82 3579.36
    > ============76_GROUP========time====================================
    > min q1 median q3 max
    > 569.65 660.155 750.66 856.245 961.83
    > ============76_NORMAL========Mop/s===================================
    > min q1 median q3 max
    > 30424.5 31486.4 31486.4 31486.4 32548.4
    > ============76_NORMAL========time====================================
    > min q1 median q3 max
    > 62.65 64.835 64.835 64.835 67.02
    >
    >
    > After (linux-5.3-rc1+ @ a1dc0446d649 + this v2 series pulled from
    > Vincent's git on ~8/15)
    >
    > lu.C.x_76_GROUP_1.stress.ps.numa.hist Average 0.36 1.00 0.64
    > lu.C.x_76_GROUP_2.stress.ps.numa.hist Average 1.00 1.00
    > lu.C.x_76_GROUP_3.stress.ps.numa.hist Average 1.00 1.00
    > lu.C.x_76_NORMAL_1.stress.ps.numa.hist Average 0.23 0.15 0.31 1.31
    > lu.C.x_76_NORMAL_2.stress.ps.numa.hist Average 1.00 0.00 0.00 1.00
    >
    > lu.C.x_76_GROUP_1.ps.numa.hist Average 18.91 18.36 18.91 19.82
    > lu.C.x_76_GROUP_2.ps.numa.hist Average 18.36 18.00 19.91 19.73
    > lu.C.x_76_GROUP_3.ps.numa.hist Average 18.17 18.42 19.25 20.17
    > lu.C.x_76_NORMAL_1.ps.numa.hist Average 19.08 20.00 18.62 18.31
    > lu.C.x_76_NORMAL_2.ps.numa.hist Average 18.09 19.91 19.18 18.82
    >
    > ============76_GROUP========Mop/s===================================
    > min q1 median q3 max
    > 32304.1 33176 34047.9 34166.8 34285.7
    > ============76_GROUP========time====================================
    > min q1 median q3 max
    > 59.47 59.68 59.89 61.505 63.12
    > ============76_NORMAL========Mop/s===================================
    > min q1 median q3 max
    > 29825.5 32454 32454 32454 35082.5
    > ============76_NORMAL========time====================================
    > min q1 median q3 max
    > 58.12 63.24 63.24 63.24 68.36
    >
    >
    > I had initially tracked this down to two issues. The first was picking the wrong
    > group in find_busiest_group due to using the average load. The second was in
    > fix_small_imbalance(). The "load" of the lu.C tasks was so low it often failed
    > to move anything even when it did find a group that was overloaded (nr_running
    > > width). I have two small patches which fix this but since Vincent was embarking
    > on a re-work which also addressed this I dropped them.
    >
    > We've also run a series of performance tests we use to check for regressions and
    > did not find any bad results on our workloads and systems.
    >
    > So...
    >
    > Tested-by: Phil Auld <pauld@redhat.com>

    Thanks for testing

    Vincent

    >
    >
    > Cheers,
    > Phil
    > --

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