Re: [PATCH v6 09/16] sched/cpufreq: uclamp: Add utilization clamping for RT tasks

Patrick Bellasi
2019-01-23T14:40:11Z

On 23-Jan 11:49, Peter Zijlstra wrote:
> On Tue, Jan 15, 2019 at 10:15:06AM +0000, Patrick Bellasi wrote:
> > @@ -858,16 +859,23 @@ static inline void
> > uclamp_effective_get(struct task_struct *p, unsigned int clamp_id,
> > unsigned int *clamp_value, unsigned int *bucket_id)
> > {
> > + struct uclamp_se *default_clamp;
> > +
> > /* Task specific clamp value */
> > *clamp_value = p->uclamp[clamp_id].value;
> > *bucket_id = p->uclamp[clamp_id].bucket_id;
> >
> > + /* RT tasks have different default values */
> > + default_clamp = task_has_rt_policy(p)
> > + ? uclamp_default_perf
> > + : uclamp_default;
> > +
> > /* System default restriction */
> > - if (unlikely(*clamp_value < uclamp_default[UCLAMP_MIN].value ||
> > - *clamp_value > uclamp_default[UCLAMP_MAX].value)) {
> > + if (unlikely(*clamp_value < default_clamp[UCLAMP_MIN].value ||
> > + *clamp_value > default_clamp[UCLAMP_MAX].value)) {
> > /* Keep it simple: unconditionally enforce system defaults */
> > - *clamp_value = uclamp_default[clamp_id].value;
> > - *bucket_id = uclamp_default[clamp_id].bucket_id;
> > + *clamp_value = default_clamp[clamp_id].value;
> > + *bucket_id = default_clamp[clamp_id].bucket_id;
> > }
> > }
>
> So I still don't much like the whole effective thing;

:/

I find back-annotation useful in many cases since we have different
sources for possible clamp values:

1. task specific
2. cgroup defined
3. system defaults
4. system power default

I don't think we can avoid to somehow back annotate on which bucket a
task has been refcounted... it makes dequeue so much easier, it helps
in ensuring that the refcouning is consistent and enable lazy updates.

> but I think you should use rt_task() instead of
> task_has_rt_policy().

Right... will do.

--
#include <best/regards.h>

Patrick Bellasi