Re: [PATCH v7 01/15] sched/core: uclamp: Add CPU's clamp buckets refcounting

Patrick Bellasi
2019-03-14T12:22:56Z

On 13-Mar 14:08, Suren Baghdasaryan wrote:
> On Wed, Mar 13, 2019 at 12:46 PM Peter Zijlstra <peterz@infradead.org> wrote:
> >
> > On Wed, Mar 13, 2019 at 03:23:59PM +0000, Patrick Bellasi wrote:
> > > On 13-Mar 15:09, Peter Zijlstra wrote:
> > > > On Fri, Feb 08, 2019 at 10:05:40AM +0000, Patrick Bellasi wrote:
> >
> > > > > +static inline void uclamp_rq_update(struct rq *rq, unsigned int clamp_id)
> > > > > +{
> > > > > + struct uclamp_bucket *bucket = rq->uclamp[clamp_id].bucket;
> > > > > + unsigned int max_value = uclamp_none(clamp_id);
> > > >
> > > > That's 1024 for uclamp_max
> > > >
> > > > > + unsigned int bucket_id;
> > > > > +
> > > > > + /*
> > > > > + * Both min and max clamps are MAX aggregated, thus the topmost
> > > > > + * bucket with some tasks defines the rq's clamp value.
> > > > > + */
> > > > > + bucket_id = UCLAMP_BUCKETS;
> > > > > + do {
> > > > > + --bucket_id;
> > > > > + if (!rq->uclamp[clamp_id].bucket[bucket_id].tasks)
> > > > > + continue;
> > > > > + max_value = bucket[bucket_id].value;
> > > >
> > > > but this will then _lower_ it. That's not a MAX aggregate.
> > >
> > > For uclamp_max we want max_value=1024 when there are no active tasks,
> > > which means: no max clamp enforced on CFS/RT "idle" cpus.
> > >
> > > If instead there are active RT/CFS tasks then we want the clamp value
> > > of the max group, which means: MAX aggregate active clamps.
> > >
> > > That's what the code above does and the comment says.
> >
> > That's (obviously) not how I read it... maybe something like:
> >
> > static inline void uclamp_rq_update(struct rq *rq, unsigned int clamp_id)
> > {
> > struct uclamp_bucket *bucket = rq->uclamp[clamp_id].bucket;
> > int i;
> >
> > /*
> > * Since both min and max clamps are max aggregated, find the
> > * top most bucket with tasks in.
> > */
> > for (i = UCLMAP_BUCKETS-1; i>=0; i--) {
> > if (!bucket[i].tasks)
> > continue;
> > return bucket[i].value;
> > }
> >
> > /* No tasks -- default clamp values */
> > return uclamp_none(clamp_id);
> > }
> >
> > would make it clearer?
>
> This way it's also more readable/obvious when it's used inside
> uclamp_rq_dec_id, assuming uclamp_rq_update is renamed into smth like
> get_max_rq_uclamp.

Rightm, I have now something like that:

---8<---
static inline unsigned int uclamp_rq_max_value(struct rq *rq, unsigned int clamp_id)
{
struct uclamp_bucket *bucket = rq->uclamp[clamp_id].bucket;
int bucket_id;

/*
* Since both min and max clamps are max aggregated, find the
* top most bucket with tasks in.
*/
for (bucket_id = UCLMAP_BUCKETS-1; bucket_id >= 0; bucket_id--) {
if (!bucket[bucket_id].tasks)
continue;
return bucket[bucket_id].value;
}

/* No tasks -- default clamp value */
return uclamp_none(clamp_id);
}

static inline void uclamp_rq_dec_id(struct task_struct *p, struct rq *rq,
unsigned int clamp_id)
{
//...
if (bucket->value >= rq_clamp) {
/*
* Reset rq's clamp bucket value to its nominal value whenever
* there are anymore RUNNABLE tasks refcounting it.
*/
bucket->value = uclamp_bucket_nominal_value(rq_clamp);
WRITE_ONCE(uc_rq->value, uclamp_rq_max_value(rq, clamp_id));
}
}
---8<---

--
#include <best/regards.h>

Patrick Bellasi