linux-kernel - Re: [RFC v3 1/6] Track the active utilisation

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Message-ID: <de0b4be7-5481-e4c7-f1eb-298ebd677b8f@redhat.com>
Date:   Tue, 25 Oct 2016 11:09:52 +0200
From:   Daniel Bristot de Oliveira <bristot@...hat.com>
To:     Luca Abeni <luca.abeni@...tn.it>, linux-kernel@...r.kernel.org
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Juri Lelli <juri.lelli@....com>,
        Claudio Scordino <claudio@...dence.eu.com>,
        Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [RFC v3 1/6] Track the active utilisation

Il 24/10/2016 16:06, Luca Abeni ha scritto:
> The active utilisation here is defined as the total utilisation of the
> 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),
> 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...)
> 
> 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.
> 
> 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;
> +}

why not...

static *inline*
void add_running_bw(struct sched_dl_entity *dl_se, struct dl_rq *dl_rq)
{
	dl_rq->running_bw += dl_se->dl_bw;
}

am I missing something?

> +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;
> +}

(if I am not missing anything...)

the same in the above function: use inline and remove the se_bw variable.

-- Daniel