Re: [PATCH v3 06/14] sched/cpufreq: uclamp: add utilization clamping for RT tasks

Patrick Bellasi
2018-08-09T15:34:23Z

On 07-Aug 15:26, Juri Lelli wrote:
> Hi,
>
> On 06/08/18 17:39, Patrick Bellasi wrote:
>
> [...]
>
> > @@ -223,13 +224,25 @@ static unsigned long sugov_get_util(struct sugov_cpu *sg_cpu)
> > * utilization (PELT windows are synchronized) we can directly add them
> > * to obtain the CPU's actual utilization.
> > *
> > - * CFS utilization can be boosted or capped, depending on utilization
> > - * clamp constraints configured for currently RUNNABLE tasks.
> > + * CFS and RT utilizations can be boosted or capped, depending on
> > + * utilization constraints enforce by currently RUNNABLE tasks.
> > + * They are individually clamped to ensure fairness across classes,
> > + * meaning that CFS always gets (if possible) the (minimum) required
> > + * bandwidth on top of that required by higher priority classes.
>
> Is this a stale comment written before UCLAMP_SCHED_CLASS was
> introduced? It seems to apply to the below if branch only.

Yes, you right... I'll update the comment.

> > */
> > - util = cpu_util_cfs(rq);
> > - if (util)
> > - util = uclamp_util(cpu_of(rq), util);
> > - util += cpu_util_rt(rq);
> > + util_cfs = cpu_util_cfs(rq);
> > + util_rt = cpu_util_rt(rq);
> > + if (sched_feat(UCLAMP_SCHED_CLASS)) {
> > + util = 0;
> > + if (util_cfs)
> > + util += uclamp_util(cpu_of(rq), util_cfs);
> > + if (util_rt)
> > + util += uclamp_util(cpu_of(rq), util_rt);
> > + } else {
> > + util = cpu_util_cfs(rq);
> > + util += cpu_util_rt(rq);
> > + util = uclamp_util(cpu_of(rq), util);
> > + }

Regarding the two policies, do you have any comment?

We had an internal discussion and we found pro/cons for both... but
I'm not sure keeping the sched_feat is a good solution on the long
run, i.e. mainline merge ;)

--
#include <best/regards.h>

Patrick Bellasi