Re: [PATCH v5 4/4] sched/fair: update util_est only on util_avg updates

[Peter Zijlstra]

On Wed, Mar 07, 2018 at 11:38:52AM +0100, Peter Zijlstra wrote:
> On Thu, Feb 22, 2018 at 05:01:53PM +0000, Patrick Bellasi wrote:

> > @@ -5218,7 +5242,7 @@ static inline void util_est_enqueue(struct cfs_rq *cfs_rq,
> >  
> >  	/* Update root cfs_rq's estimated utilization */
> >  	enqueued  = READ_ONCE(cfs_rq->avg.util_est.enqueued);
> > -	enqueued += _task_util_est(p);
> > +	enqueued += (_task_util_est(p) | 0x1);
> 
> UTIL_EST_NEED_UPDATE_FLAG, although I do agree that 0x1 is much easier
> to type ;-)
> 
> But you set it for the cfs_rq value ?! That doesn't seem right.
> 
> >  	WRITE_ONCE(cfs_rq->avg.util_est.enqueued, enqueued);
> >  }
> >  
> > @@ -5310,7 +5334,7 @@ static inline void util_est_dequeue(struct cfs_rq *cfs_rq,
> >  	if (cfs_rq->nr_running) {
> >  		ue.enqueued  = READ_ONCE(cfs_rq->avg.util_est.enqueued);
> >  		ue.enqueued -= min_t(unsigned int, ue.enqueued,
> > -				     _task_util_est(p));
> > +				     (_task_util_est(p) | UTIL_EST_NEED_UPDATE_FLAG));
> >  	}
> >  	WRITE_ONCE(cfs_rq->avg.util_est.enqueued, ue.enqueued);
> >  

OK, so you unconditionally set that bit here to make the add/sub match.
Clearly I wasn't having a good day yesterday.