Date: Tue, 5 Apr 2016 14:42:18 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Luca Abeni <luca.abeni@unitn.it>
Cc: linux-kernel@vger.kernel.org, Ingo Molnar <mingo@redhat.com>,
        Juri Lelli <juri.lelli@arm.com>
Subject: Re: [RFC v2 3/7] Improve the tracking of active utilisation
Message-ID: <20160405124218.GW3430@twins.programming.kicks-ass.net>
References: <1459523553-29089-1-git-send-email-luca.abeni@unitn.it>
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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 ?