Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1365645

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

Show all headers | View raw

On 03/28/2016 11:30 AM, Dietmar Eggemann wrote:
> On 03/28/2016 06:34 PM, Steve Muckle wrote:
>> Hi Dietmar,
>>
>> On 03/28/2016 05:02 AM, Dietmar Eggemann wrote:
>>> Hi Steve,
>>>
>>> these patches fall into the bucket of 'optimization of updating the
>>> value only if the root cfs_rq util has changed' as discussed in '[PATCH
>>> 5/8] sched/cpufreq: pass sched class into cpufreq_update_util' of Mike
>>> T's current series '[PATCH 0/8] schedutil enhancements', right?
>>
>> I would say just the second patch is an optimization. The first and
>> third patches cover additional paths in CFS where the hook should be
>> called but currently is not, which I think is a correctness issue.
> 
> Not disagreeing here but I don't know if this level of accuracy is
> really needed. I mean we currently miss updates in
> enqueue_task_fair()->enqueue_entity()->enqueue_entity_load_avg() and
> idle_balance()/rebalance_domains()->update_blocked_averages() but there
> are plenty of call sides of update_load_avg(se, ...) with
> '&rq_of(cfs_rq_of(se))->cfs == cfs_rq_of(se)'.
>
> The question for me is does schedutil work better with this new, more
> accurate signal? IMO, not receiving a bunch of consecutive
> cpufreq_update_util's w/ the same 'util' value is probably a good thing,
> unless we see the interaction with RT/DL class as mentioned by Sai. Here
> an agreement on the design for the 'capacity vote aggregation from
> CFS/RT/DL' would help to clarify.

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...

thanks,
Steve

Back to linux.kernel | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

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

csiph-web