Re: [RFC v2 3/7] Improve the tracking of active utilisation

Peter Zijlstra
2016-04-05T12:42:24Z

On Fri, Apr 01, 2016 at 05:12:29PM +0200, Luca Abeni wrote:
> +static void task_go_inactive(struct task_struct *p)
> +{
> + struct sched_dl_entity *dl_se = &p->dl;
> + struct hrtimer *timer = &dl_se->inactive_timer;
> + struct dl_rq *dl_rq = dl_rq_of_se(dl_se);
> + struct rq *rq = rq_of_dl_rq(dl_rq);
> + ktime_t now, act;
> + s64 delta;
> + u64 zerolag_time;

s64 zerolag_time;

> +
> + WARN_ON(dl_se->dl_runtime == 0);
> +
> + /* If the inactive timer is already armed, return immediately */
> + if (hrtimer_active(&dl_se->inactive_timer))
> + return;
> +
> +
> + /*
> + * We want the timer to fire at the "0 lag time", but considering
> + * that it is actually coming from rq->clock and not from
> + * hrtimer's time base reading.
> + */
> + zerolag_time = dl_se->deadline -
> + div64_long((dl_se->runtime * dl_se->dl_period),
> + dl_se->dl_runtime);
> +
> + act = ns_to_ktime(zerolag_time);
> + now = hrtimer_cb_get_time(timer);
> + delta = ktime_to_ns(now) - rq_clock(rq);
> + act = ktime_add_ns(act, delta);

Would something like:

zerolag_time -= rq_clock(rq);

> +
> + /*
> + * If the "0-lag time" already passed, decrease the active
> + * utilization now, instead of starting a timer
> + */
> + if (ktime_us_delta(act, now) < 0) {

if (zerolag_time < 0)

> + sub_running_bw(dl_se, dl_rq);
> + if (!dl_task(p))
> + __dl_clear_params(p);
> +
> + return;
> + }
> +
> + get_task_struct(p);
> + hrtimer_start(timer, act, HRTIMER_MODE_ABS);

hrtimer_start(timer, ns_to_ktime(zerolag), HRTIMER_MODE_REL);

> +}

Not be simpler ?