Re: [PATCH v6 06/11] cpufreq/schedutil: use dl utilization tracking

[Vincent Guittot]

On 8 June 2018 at 15:36, Juri Lelli <juri.lelli@xxxxxxxxxx> wrote:
> On 08/06/18 14:54, Juri Lelli wrote:
>> On 08/06/18 14:48, Vincent Guittot wrote:
>> > On 8 June 2018 at 14:39, Juri Lelli <juri.lelli@xxxxxxxxxx> wrote:
>> > > Hi Vincent,
>> > >
>> > > On 08/06/18 14:09, Vincent Guittot wrote:
>> > >> Now that we have both the dl class bandwidth requirement and the dl class
>> > >> utilization, we can detect when CPU is fully used so we should run at max.
>> > >> Otherwise, we keep using the dl bandwidth requirement to define the
>> > >> utilization of the CPU
>> > >>
>> > >> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
>> > >> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
>> > >> Signed-off-by: Vincent Guittot <vincent.guittot@xxxxxxxxxx>
>> > >> ---
>> > >
>> > > [...]
>> > >
>> > >> @@ -190,20 +192,24 @@ static unsigned long sugov_aggregate_util(struct sugov_cpu *sg_cpu)
>> > >>       if (rq->rt.rt_nr_running)
>> > >>               return sg_cpu->max;
>> > >>
>> > >> -     util = sg_cpu->util_dl;
>> > >> -     util += sg_cpu->util_cfs;
>> > >> +     util = sg_cpu->util_cfs;
>> > >>       util += sg_cpu->util_rt;
>> > >>
>> > >> +     if ((util + sg_cpu->util_dl) >= sg_cpu->max)
>> > >> +             return sg_cpu->max;
>> > >> +
>> > >
>> > > Mmm, won't we run at max (or reach max) with a, say, 100ms/500ms DL task
>> > > running alone?
>> >
>> > not for a 100ms running task. You have to run more than 320ms to reach max value
>> >
>> > 100ms/500ms will vary between 0 and 907
>>
>> OK, right, my point I guess is still that such a task will run fine at
>> ~250 and it might be save more energy by doing so?
>
> As discussed on IRC, we still endup selecting 1/5 of max freq because
> util_dl is below max.
>
> So, turning point is at ~320ms/[something_bigger], which looks a pretty
> big runtime, but I'm not sure if having that is OK. Also, it becomes
> smaller with CFS/RT background "perturbations". Mmm.
>
> BTW, adding Luca and Claudio. :)

Argh... I have added few more but forgot Luca and Claudio. I'm very sorry