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    SubjectRe: [PATCH 2/2] sched/fair: Always propagate runnable_load_avg
    Hello,

    On Mon, May 01, 2017 at 05:56:13PM +0200, Peter Zijlstra wrote:
    > On Fri, Apr 28, 2017 at 04:33:47PM -0400, Tejun Heo wrote:
    > > I'm attaching the debug patch. With your change (avg instead of
    > > runnable_avg), the following trace shows why it's wrong.
    >
    > Ah, OK. So you really want runnable_avg (and I understand why), which is
    > rather unfortunate, since we have everything on load_avg.
    >
    > So for shares, load_avg gives a more stable number. This is important
    > since tg->load_avg is a global number, so computing it is expensive (and
    > slow). Therefore more stable numbers are good.
    >
    > > The thing with cfs_rq se's load_avg is that, it isn't really used
    > > anywhere else AFAICS, so overriding it to the cfs_rq's
    > > runnable_load_avg isn't prettiest but doesn't really change anything.
    >
    > You mean, consistently expressing a group's se->load.weight in terms of
    > runnable_load_avg? See the above.

    I think you got this on the other thread but for clarity:

    cfs_rq->avg.load_avg is used for share calculation and we want to keep
    it that way as the calcluation is expensive and rather decoupled
    across CPUs (the deviation can be quite a bit without the stability).
    But the group *se*->avg.load_avg is a separate thing which isn't
    really used anywhere except for as a propagation channel from group
    cfs_rq to its parent cfs_rq.

    Thanks.

    --
    tejun

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