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

[Peter Zijlstra]

On Wed, Mar 13, 2019 at 03:59:54PM +0000, Patrick Bellasi wrote:
> On 13-Mar 14:52, Peter Zijlstra wrote:
> > > +static inline void uclamp_rq_dec_id(struct task_struct *p, struct rq *rq,
> > > +				    unsigned int clamp_id)
> > > +{
> > > +	unsigned int bucket_id = p->uclamp[clamp_id].bucket_id;
> > > +	unsigned int rq_clamp, bkt_clamp;
> > > +
> > > +	SCHED_WARN_ON(!rq->uclamp[clamp_id].bucket[bucket_id].tasks);
> > > +	if (likely(rq->uclamp[clamp_id].bucket[bucket_id].tasks))
> > > +		rq->uclamp[clamp_id].bucket[bucket_id].tasks--;
> > > +
> > > +	/*
> > > +	 * Keep "local clamping" simple and accept to (possibly) overboost
> > > +	 * still RUNNABLE tasks in the same bucket.
> > > +	 */
> > > +	if (likely(rq->uclamp[clamp_id].bucket[bucket_id].tasks))
> > > +		return;
> > 
> > (Oh man, I hope that generates semi sane code; long live CSE passes I
> > suppose)
> 
> What do you mean ?

that does: 'rq->uclamp[clamp_id].bucket[bucket_id].tasks' three times in
a row. And yes the compiler _should_ dtrt, but....