On Tue, Jan 23, 2018 at 06:08:45PM +0000, Patrick Bellasi wrote:
> +static inline void util_est_dequeue(struct task_struct *p, int flags)
> +{
> + struct cfs_rq *cfs_rq = &task_rq(p)->cfs;
> + unsigned long util_last = task_util(p);
> + bool sleep = flags & DEQUEUE_SLEEP;
> + unsigned long ewma;
> + long util_est = 0;
> +
> + 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.
> + */
> + if (cfs_rq->nr_running) {
> + util_est = READ_ONCE(cfs_rq->util_est_runnable);
> + util_est -= min_t(long, util_est, task_util_est(p));
> + }
> + WRITE_ONCE(cfs_rq->util_est_runnable, util_est);
> +
> + /*
> + * Skip update of task's estimated utilization when the task has not
> + * yet completed an activation, e.g. being migrated.
> + */
> + if (!sleep)
> + return;
> +
Since you only use sleep once, you might as well write it out there.
Also, does GCC lower the task_util() eval to here?
> + /*
> + * Skip update of task's estimated utilization when its EWMA is
> already
> + * ~1% close to its last activation value.
> + */
> + util_est = p->util_est.ewma;
> + if (abs(util_est - util_last) <= (SCHED_CAPACITY_SCALE / 100))
> + return;
Aside from that being whitespace challenged, did you also try:
if ((unsigned)((util_est - util_last) + LIM - 1) < (2 * LIM - 1))
Also, since we only care about the absolute value; we could use:
util_last - ewma
here (note the above also forgets to use READ_ONCE), and reuse the result:
> +
> + /*
> + * Update Task's estimated utilization
> + *
> + * When *p completes an activation we can consolidate another sample
> + * about the task size. This is done by storing the last PELT value
> + * for this task and using this value to load another sample in the
> + * exponential weighted moving average:
> + *
> + * 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) / w - ewma(t-1))
> + *
> + * Where 'w' is the weight of new samples, which is configured to be
> + * 0.25, thus making w=1/4
> + */
> + p->se.avg.util_est.last = util_last;
> + ewma = READ_ONCE(p->se.avg.util_est.ewma);
> + ewma = util_last + (ewma << UTIL_EST_WEIGHT_SHIFT) - ewma;
here.
> + ewma >>= UTIL_EST_WEIGHT_SHIFT;
> + WRITE_ONCE(p->se.avg.util_est.ewma, ewma);
> +}
So something along these lines:
ewma = READ_ONCE(p->se.avg.util_est.ewma);
diff = util_last - ewma;
if ((unsigned)(diff + LIM - 1) < (2 * LIM - 1))
return;
p->se.avg.util_est.last = util_last;
ewma = (diff + (ewma << EWMA_SHIFT)) >> EWMA_SHIFT;
WRITE_ONCE(p->se.avg.util_est.ewma, ewma);
Make sense?
