Messages in this thread | | | From | Vincent Guittot <> | Date | Wed, 1 Mar 2023 11:39:06 +0100 | Subject | Re: [RFC PATCH 0/1] sched/pelt: Change PELT halflife at runtime |
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On Thu, 23 Feb 2023 at 16:37, Qais Yousef <qyousef@layalina.io> wrote: > > On 02/09/23 17:16, Vincent Guittot wrote: > > > I don't see how util_est_faster can help this 1ms task here ? It's > > most probably never be preempted during this 1ms. For such an Android > > Graphics Pipeline short task, hasn't uclamp_min been designed for and > > a better solution ? > > uclamp_min is being used in UI and helping there. But your mileage might vary > with adoption still. > > The major motivation behind this is to help things like gaming as the original > thread started. It can help UI and other use cases too. Android framework has > a lot of context on the type of workload that can help it make a decision when > this helps. And OEMs can have the chance to tune and apply based on the > characteristics of their device. > > > IIUC how util_est_faster works, it removes the waiting time when > > sharing cpu time with other tasks. So as long as there is no (runnable > > but not running time), the result is the same as current util_est. > > util_est_faster makes a difference only when the task alternates > > between runnable and running slices. > > Have you considered using runnable_avg metrics in the increase of cpu > > freq ? This takes into the runnable slice and not only the running > > time and increase faster than util_avg when tasks compete for the same > > CPU > > Just to understand why we're heading into this direction now. > > AFAIU the desired outcome to have faster rampup time (and on HMP faster up > migration) which both are tied to utilization signal. > > Wouldn't make the util response time faster help not just for rampup, but > rampdown too? > > If we improve util response time, couldn't this mean we can remove util_est or > am I missing something?
not sure because you still have a ramping step whereas util_est directly gives you the final tager
> > Currently we have util response which is tweaked by util_est and then that is > tweaked further by schedutil with that 25% margin when maping util to > frequency.
the 25% is not related to the ramping time but to the fact that you always need some margin to cover unexpected events and estimation error
> > I think if we can allow improving general util response time by tweaking PELT > HALFLIFE we can potentially remove util_est and potentially that magic 25% > margin too. > > Why the approach of further tweaking util_est is better?
note that in this case it doesn't really tweak util_est but Dietmar has taken into account runnable_avg to increase the freq in case of contention
Also IIUC Dietmar's results, the problem seems more linked to the selection of a higher freq than increasing the utilization; runnable_avg tests give similar perf results than shorter half life and better power consumption.
> > Recently phoronix reported that schedutil behavior is suboptimal and I wonder > if the response time is contributing to that > > https://www.phoronix.com/review/schedutil-quirky-2023 > > > Cheers > > -- > Qais Yousef
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