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    SubjectRe: [PATCH v5 1/4] sched/fair: add util_est on top of PELT
    On Thu, Feb 22, 2018 at 05:01:50PM +0000, Patrick Bellasi wrote:
    > +static inline void util_est_enqueue(struct cfs_rq *cfs_rq,
    > + struct task_struct *p)
    > +{
    > + unsigned int enqueued;
    > +
    > + if (!sched_feat(UTIL_EST))
    > + return;
    > +
    > + /* Update root cfs_rq's estimated utilization */
    > + enqueued = READ_ONCE(cfs_rq->avg.util_est.enqueued);
    > + enqueued += _task_util_est(p);
    > + WRITE_ONCE(cfs_rq->avg.util_est.enqueued, enqueued);
    > +}

    > +static inline void util_est_dequeue(struct cfs_rq *cfs_rq,
    > + struct task_struct *p,
    > + bool task_sleep)
    > +{
    > + long last_ewma_diff;
    > + struct util_est ue;
    > +
    > + if (!sched_feat(UTIL_EST))
    > + return;
    > +
    > + /*
    > + * Update root cfs_rq's estimated utilization
    > + *
    > + * If *p is the last task then the root cfs_rq's estimated utilization
    > + * of a CPU is 0 by definition.
    > + */
    > + ue.enqueued = 0;
    > + 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));
    > + }
    > + WRITE_ONCE(cfs_rq->avg.util_est.enqueued, ue.enqueued);

    It appears to me this isn't a stable situation and completely relies on
    the !nr_running case to recalibrate. If we ensure that doesn't happen
    for a significant while the sum can run-away, right?

    Should we put a max in enqueue to avoid this?

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