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

[Patrick Bellasi]

On 13-Mar 15:09, Peter Zijlstra wrote:
> On Fri, Feb 08, 2019 at 10:05:40AM +0000, Patrick Bellasi wrote:
> > +static inline unsigned int uclamp_none(int clamp_id)
> > +{
> > +	if (clamp_id == UCLAMP_MIN)
> > +		return 0;
> > +	return SCHED_CAPACITY_SCALE;
> > +}
> > +
> > +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.

> > +		break;
> > +	} while (bucket_id);
> > +
> > +	WRITE_ONCE(rq->uclamp[clamp_id].value, max_value);
> > +}

-- 
#include <best/regards.h>

Patrick Bellasi