Re: [PATCH 1/2] sched/fair: move cpufreq hook to update_cfs_rq_load_avg()

From	Peter Zijlstra <peterz@infradead.org>
Newsgroups	linux.kernel
Subject	Re: [PATCH 1/2] sched/fair: move cpufreq hook to update_cfs_rq_load_avg()
Date	2016-03-30 21:40 +0200
Message-ID	<riu89-1FR-7@gated-at.bofh.it> (permalink)
References	<rfimR-4U6-13@gated-at.bofh.it> <rhImS-1aq-17@gated-at.bofh.it> <rhImS-1aq-15@gated-at.bofh.it> <rhLb3-36F-13@gated-at.bofh.it> <rhLb3-36F-11@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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On Mon, Mar 28, 2016 at 12:38:26PM -0700, Steve Muckle wrote:
> Without covering all the paths where CFS utilization changes it's
> possible to have to wait up to a tick to act on some changes, since the
> tick is the only guaranteed regularly-occurring instance of the hook.
> That's an unacceptable amount of latency IMO...

Note that even with your patches that might still be the case. Remote
wakeups might not happen on the destination CPU at all, so it might not
be until the next tick (which always happens locally) that we'll
'observe' the utilization change brought with the wakeups.

We could force all the remote wakeups to IPI the destination CPU, but
that comes at a significant performance cost.

Thread

[PATCH 1/2] sched/fair: move cpufreq hook to update_cfs_rq_load_avg() Steve Muckle <steve.muckle@linaro.org> - 2016-03-22 01:30 +0100
  Re: [PATCH 1/2] sched/fair: move cpufreq hook to  update_cfs_rq_load_avg() Steve Muckle <steve.muckle@linaro.org> - 2016-03-28 18:40 +0200
    Re: [PATCH 1/2] sched/fair: move cpufreq hook to  update_cfs_rq_load_avg() Steve Muckle <steve.muckle@linaro.org> - 2016-03-28 21:40 +0200
      Re: [PATCH 1/2] sched/fair: move cpufreq hook to  update_cfs_rq_load_avg() Peter Zijlstra <peterz@infradead.org> - 2016-03-30 21:40 +0200
        Re: [PATCH 1/2] sched/fair: move cpufreq hook to  update_cfs_rq_load_avg() Steve Muckle <steve.muckle@linaro.org> - 2016-03-31 03:50 +0200
          Re: [PATCH 1/2] sched/fair: move cpufreq hook to  update_cfs_rq_load_avg() Peter Zijlstra <peterz@infradead.org> - 2016-03-31 09:40 +0200
            Re: [PATCH 1/2] sched/fair: move cpufreq hook to  update_cfs_rq_load_avg() Steve Muckle <steve.muckle@linaro.org> - 2016-03-31 23:30 +0200
              Re: [PATCH 1/2] sched/fair: move cpufreq hook to  update_cfs_rq_load_avg() Peter Zijlstra <peterz@infradead.org> - 2016-04-01 11:30 +0200
        Re: [PATCH 1/2] sched/fair: move cpufreq hook to update_cfs_rq_load_avg() Vincent Guittot <vincent.guittot@linaro.org> - 2016-03-31 11:30 +0200
          Re: [PATCH 1/2] sched/fair: move cpufreq hook to  update_cfs_rq_load_avg() Peter Zijlstra <peterz@infradead.org> - 2016-03-31 11:40 +0200
            Re: [PATCH 1/2] sched/fair: move cpufreq hook to update_cfs_rq_load_avg() Vincent Guittot <vincent.guittot@linaro.org> - 2016-03-31 12:00 +0200
              Re: [PATCH 1/2] sched/fair: move cpufreq hook to  update_cfs_rq_load_avg() Peter Zijlstra <peterz@infradead.org> - 2016-03-31 12:50 +0200
                Re: [PATCH 1/2] sched/fair: move cpufreq hook to update_cfs_rq_load_avg() Vincent Guittot <vincent.guittot@linaro.org> - 2016-03-31 14:20 +0200
                Re: [PATCH 1/2] sched/fair: move cpufreq hook to  update_cfs_rq_load_avg() Peter Zijlstra <peterz@infradead.org> - 2016-03-31 14:40 +0200
                Re: [PATCH 1/2] sched/fair: move cpufreq hook to update_cfs_rq_load_avg() Vincent Guittot <vincent.guittot@linaro.org> - 2016-03-31 15:00 +0200

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