Re: [PATCH v3 09/14] sched/core: uclamp: propagate parent clamps

Patrick Bellasi
2018-08-16T14:07:31Z

On 16-Aug 14:39, Pavan Kondeti wrote:
> On Mon, Aug 06, 2018 at 05:39:41PM +0100, Patrick Bellasi wrote:

[...]

> > diff --git a/include/linux/sched.h b/include/linux/sched.h
> > index 8f48e64fb8a6..3fac2d098084 100644
> > --- a/include/linux/sched.h
> > +++ b/include/linux/sched.h
> > @@ -589,6 +589,11 @@ struct uclamp_se {
> > unsigned int value;
> > /* Utilization clamp group for this constraint */
> > unsigned int group_id;
> > + /* Effective clamp for tasks in this group */
> > + struct {
> > + unsigned int value;
> > + unsigned int group_id;
> > + } effective;
> > };
>
> Are these needed when CONFIG_UCLAMP_TASK_GROUP is disabled?

Mmm... not entirely, at least not the value.

While working on v4 I've notice that:

(1) task_struct::uclamp::effective::group_id

can be used for the back annotation we add in:

[PATCH v3 11/14] sched/core: uclamp: use TG's clamps to restrict Task's clamps

using the additional field:

(2) task_struct::uclamp_group_id

So, I'm updating that patch to re-use (1) instead of adding (2).

Regarding:

(3) task_struct::uclamp::effective::value

it can be used to track the task's effective clamp value once I add
the discretization support discussed with Juri in:

https://lore.kernel.org/lkml/20180809152313.lewfhufidhxb2qrk@darkstar/

So, I would say that in v4 I can try to see if and how we can guard
(some of) the effective values on !CONFIG_UCLAMP_TASK_GROUP
configurations...

>
> > union rcu_special {
> > diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> > index 2ba55a4afffb..f692df3787bd 100644
> > --- a/kernel/sched/core.c
> > +++ b/kernel/sched/core.c
> > @@ -1237,6 +1237,8 @@ static inline void init_uclamp_sched_group(void)
> > uc_se = &root_task_group.uclamp[clamp_id];
> > uc_se->value = uclamp_none(clamp_id);
> > uc_se->group_id = group_id;
> > + uc_se->effective.value = uclamp_none(clamp_id);
> > + uc_se->effective.group_id = group_id;
> >
> > /* Attach root TG's clamp group */
> > uc_map[group_id].se_count = 1;
> >
>
> <snip>
>
> > @@ -7622,11 +7687,19 @@ static struct cftype cpu_legacy_files[] = {
> > .read_u64 = cpu_util_min_read_u64,
> > .write_u64 = cpu_util_min_write_u64,
> > },
> > + {
> > + .name = "util.min.effective",
> > + .read_u64 = cpu_util_min_effective_read_u64,
> > + },
> > {
> > .name = "util.max",
> > .read_u64 = cpu_util_max_read_u64,
> > .write_u64 = cpu_util_max_write_u64,
> > },
> > + {
> > + .name = "util.max.effective",
> > + .read_u64 = cpu_util_max_effective_read_u64,
> > + },
> > #endif
> > { } /* Terminate */
> > };
>
> Is there any reason why these are not added for the default hierarchy?

Not really, good point!

I think I've just forgot them... which makes me notice that I still
have to improve the coverage for my tests on the default hierarchy.

I don't expect big difference, since the behaviors should be the
same but...

Thanks for pointing this out... will had the attributes in the
upcoming v4.

Cheers,
Patrick

--
#include <best/regards.h>

Patrick Bellasi