On 27/11/2023 15:32, Vincent Guittot wrote: > With UTIL_EST_FASTUP now being permanent, we can take advantage of the > fact that the ewma jumps directly to a higher utilization at dequeue to > simplify util_est and remove the enqueued field. > Did some simple test with a ramp-up/ramp_down (10-80-10%) task affine to a CPU. https://nbviewer.org/github/deggeman/lisa/blob/ipynbs/ipynb/scratchpad/util_est_fastup.ipynb LGTM. [...] > @@ -4879,27 +4865,22 @@ static inline void util_est_update(struct cfs_rq *cfs_rq, > * Skip update of task's estimated utilization when its members are > * already ~1% close to its last activation value. > */ > - last_ewma_diff = ue.enqueued - ue.ewma; > - last_enqueued_diff -= ue.enqueued; > - if (within_margin(last_ewma_diff, UTIL_EST_MARGIN)) { > - if (!within_margin(last_enqueued_diff, UTIL_EST_MARGIN)) > - goto done; > - > - return; > - } > + last_ewma_diff = ewma - dequeued; > + if (last_ewma_diff < UTIL_EST_MARGIN) > + goto done; > > /* > * To avoid overestimation of actual task utilization, skip updates if > * we cannot grant there is idle time in this CPU. > */ > - if (task_util(p) > arch_scale_cpu_capacity(cpu_of(rq_of(cfs_rq)))) > + if (dequeued > arch_scale_cpu_capacity(cpu_of(rq_of(cfs_rq)))) > return; Not directly related to the changes: Should we not use `goto done` here is well to rearm UTIL_AVG_UNCHANGED? > /* > * To avoid underestimate of task utilization, skip updates of EWMA if > * we cannot grant that thread got all CPU time it wanted. > */ > - if ((ue.enqueued + UTIL_EST_MARGIN) < task_runnable(p)) > + if ((dequeued + UTIL_EST_MARGIN) < task_runnable(p)) > goto done; > > > @@ -4914,18 +4895,18 @@ static inline void util_est_update(struct cfs_rq *cfs_rq, > * ewma(t) = w * task_util(p) + (1-w) * ewma(t-1) > * = w * task_util(p) + ewma(t-1) - w * ewma(t-1) > * = w * (task_util(p) - ewma(t-1)) + ewma(t-1) > - * = w * ( last_ewma_diff ) + ewma(t-1) > - * = w * (last_ewma_diff + ewma(t-1) / w) > + * = w * ( -last_ewma_diff ) + ewma(t-1) > + * = w * (-last_ewma_diff + ewma(t-1) / w) > * > * Where 'w' is the weight of new samples, which is configured to be > * 0.25, thus making w=1/4 ( >>= UTIL_EST_WEIGHT_SHIFT) > */ The text above still mentioned ue.enqueued and that we store the current PELT value ... which isn't the case anymore. > - ue.ewma <<= UTIL_EST_WEIGHT_SHIFT; > - ue.ewma += last_ewma_diff; > - ue.ewma >>= UTIL_EST_WEIGHT_SHIFT; > + ewma <<= UTIL_EST_WEIGHT_SHIFT; > + ewma -= last_ewma_diff; > + ewma >>= UTIL_EST_WEIGHT_SHIFT; > done: > - ue.enqueued |= UTIL_AVG_UNCHANGED; > - WRITE_ONCE(p->se.avg.util_est, ue); > + ewma |= UTIL_AVG_UNCHANGED; > + WRITE_ONCE(p->se.avg.util_est, ewma); > > trace_sched_util_est_se_tp(&p->se); > } [...] Reviewed-by: Dietmar Eggemann <dietmar.eggemann@xxxxxxx>
