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Message-ID: <20161101164451.GA2769@ARMvm>
Date: Tue, 1 Nov 2016 16:45:43 +0000
From: Juri Lelli <juri.lelli@....com>
To: Luca Abeni <luca.abeni@...tn.it>
Cc: linux-kernel@...r.kernel.org,
Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...hat.com>,
Claudio Scordino <claudio@...dence.eu.com>,
Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [RFC v3 1/6] Track the active utilisation
Hi,
a few nitpicks on subject and changelog and a couple of questions below.
Subject should be changed to something like
sched/deadline: track the active utilisation
On 24/10/16 16:06, Luca Abeni wrote:
> The active utilisation here is defined as the total utilisation of the
s/The active/Active/
s/here//
s/of the active/of active/
> active (TASK_RUNNING) tasks queued on a runqueue. Hence, it is increased
> when a task wakes up and is decreased when a task blocks.
>
> When a task is migrated from CPUi to CPUj, immediately subtract the task's
> utilisation from CPUi and add it to CPUj. This mechanism is implemented by
> modifying the pull and push functions.
> Note: this is not fully correct from the theoretical point of view
> (the utilisation should be removed from CPUi only at the 0 lag time),
a more theoretically sound solution will follow.
> but doing the right thing would be _MUCH_ more complex (leaving the
> timer armed when the task is on a different CPU... Inactive timers should
> be moved from per-task timers to per-runqueue lists of timers! Bah...)
I'd remove this paragraph above.
>
> The utilisation tracking mechanism implemented in this commit can be
> fixed / improved by decreasing the active utilisation at the so-called
> "0-lag time" instead of when the task blocks.
And maybe this as well, or put it as more information about the "more
theoretically sound" solution?
>
> Signed-off-by: Juri Lelli <juri.lelli@....com>
> Signed-off-by: Luca Abeni <luca.abeni@...tn.it>
> ---
> kernel/sched/deadline.c | 39 ++++++++++++++++++++++++++++++++++++++-
> kernel/sched/sched.h | 6 ++++++
> 2 files changed, 44 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
> index 37e2449..3d95c1d 100644
> --- a/kernel/sched/deadline.c
> +++ b/kernel/sched/deadline.c
> @@ -43,6 +43,22 @@ static inline int on_dl_rq(struct sched_dl_entity *dl_se)
> return !RB_EMPTY_NODE(&dl_se->rb_node);
> }
>
> +static void add_running_bw(struct sched_dl_entity *dl_se, struct dl_rq *dl_rq)
> +{
> + u64 se_bw = dl_se->dl_bw;
> +
> + dl_rq->running_bw += se_bw;
> +}
> +
> +static void sub_running_bw(struct sched_dl_entity *dl_se, struct dl_rq *dl_rq)
> +{
> + u64 se_bw = dl_se->dl_bw;
> +
> + dl_rq->running_bw -= se_bw;
> + if (WARN_ON(dl_rq->running_bw < 0))
> + dl_rq->running_bw = 0;
> +}
> +
> static inline int is_leftmost(struct task_struct *p, struct dl_rq *dl_rq)
> {
> struct sched_dl_entity *dl_se = &p->dl;
> @@ -498,6 +514,8 @@ static void update_dl_entity(struct sched_dl_entity *dl_se,
> struct dl_rq *dl_rq = dl_rq_of_se(dl_se);
> struct rq *rq = rq_of_dl_rq(dl_rq);
>
> + add_running_bw(dl_se, dl_rq);
> +
> if (dl_time_before(dl_se->deadline, rq_clock(rq)) ||
> dl_entity_overflow(dl_se, pi_se, rq_clock(rq))) {
> dl_se->deadline = rq_clock(rq) + pi_se->dl_deadline;
> @@ -947,14 +965,19 @@ static void enqueue_task_dl(struct rq *rq, struct task_struct *p, int flags)
> return;
> }
>
> + if (p->on_rq == TASK_ON_RQ_MIGRATING)
> + add_running_bw(&p->dl, &rq->dl);
> +
> /*
> * If p is throttled, we do nothing. In fact, if it exhausted
> * its budget it needs a replenishment and, since it now is on
> * its rq, the bandwidth timer callback (which clearly has not
> * run yet) will take care of this.
> */
> - if (p->dl.dl_throttled && !(flags & ENQUEUE_REPLENISH))
> + if (p->dl.dl_throttled && !(flags & ENQUEUE_REPLENISH)) {
> + add_running_bw(&p->dl, &rq->dl);
Don't rememeber if we discussed this already, but do we need to add the bw here
even if the task is not actually enqueued until after the replenishment timer
fires?
> return;
> + }
>
> enqueue_dl_entity(&p->dl, pi_se, flags);
>
> @@ -972,6 +995,12 @@ static void dequeue_task_dl(struct rq *rq, struct task_struct *p, int flags)
> {
> update_curr_dl(rq);
> __dequeue_task_dl(rq, p, flags);
> +
> + if (p->on_rq == TASK_ON_RQ_MIGRATING)
> + sub_running_bw(&p->dl, &rq->dl);
> +
> + if (flags & DEQUEUE_SLEEP)
> + sub_running_bw(&p->dl, &rq->dl);
> }
>
> /*
> @@ -1501,7 +1530,9 @@ static int push_dl_task(struct rq *rq)
> }
>
> deactivate_task(rq, next_task, 0);
> + sub_running_bw(&next_task->dl, &rq->dl);
> set_task_cpu(next_task, later_rq->cpu);
> + add_running_bw(&next_task->dl, &later_rq->dl);
> activate_task(later_rq, next_task, 0);
> ret = 1;
>
> @@ -1589,7 +1620,9 @@ static void pull_dl_task(struct rq *this_rq)
> resched = true;
>
> deactivate_task(src_rq, p, 0);
> + sub_running_bw(&p->dl, &src_rq->dl);
> set_task_cpu(p, this_cpu);
> + add_running_bw(&p->dl, &this_rq->dl);
> activate_task(this_rq, p, 0);
> dmin = p->dl.deadline;
>
> @@ -1695,6 +1728,9 @@ static void switched_from_dl(struct rq *rq, struct task_struct *p)
> if (!start_dl_timer(p))
> __dl_clear_params(p);
>
> + if (task_on_rq_queued(p))
> + sub_running_bw(&p->dl, &rq->dl);
> +
> /*
> * Since this might be the only -deadline task on the rq,
> * this is the right place to try to pull some other one
> @@ -1712,6 +1748,7 @@ static void switched_from_dl(struct rq *rq, struct task_struct *p)
> */
> static void switched_to_dl(struct rq *rq, struct task_struct *p)
> {
> + add_running_bw(&p->dl, &rq->dl);
>
> /* If p is not queued we will update its parameters at next wakeup. */
> if (!task_on_rq_queued(p))
Don't we also need to remove bw in task_dead_dl()?
Thanks,
- Juri
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