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Date: Sat, 11 Feb 2017 08:12:37 +0100
From: luca abeni <luca.abeni@santannapisa.it>
To: Daniel Bristot de Oliveira <bristot@redhat.com>
Cc: linux-kernel@vger.kernel.org, Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>, Juri Lelli <juri.lelli@arm.com>,
        Tommaso Cucinotta <tommaso.cucinotta@sssup.it>,
        Steven Rostedt <rostedt@goodmis.org>
Subject: Re: [PATCH 1/2] sched/deadline: Replenishment timer should fire in
 the next period
Message-ID: <20170211081237.0a9208be@sweethome>
In-Reply-To: <77018c2ce2a17342b5d17cdb50209e667800b09a.1486754348.git.bristot@redhat.com>
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        <77018c2ce2a17342b5d17cdb50209e667800b09a.1486754348.git.bristot@redhat.com>
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Hi Daniel,

On Fri, 10 Feb 2017 20:48:10 +0100
Daniel Bristot de Oliveira <bristot@redhat.com> wrote:

[...]
> diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
> index 70ef2b1..3c94d85 100644
> --- a/kernel/sched/deadline.c
> +++ b/kernel/sched/deadline.c
> @@ -505,10 +505,15 @@ static void update_dl_entity(struct
> sched_dl_entity *dl_se, }
>  }
>  
> +static inline u64 dl_next_period(struct sched_dl_entity *dl_se)
> +{
> +	return dl_se->deadline - dl_se->dl_deadline +
> dl_se->dl_period; +}
> +
>  /*
>   * If the entity depleted all its runtime, and if we want it to sleep
>   * while waiting for some new execution time to become available, we
> - * set the bandwidth enforcement timer to the replenishment instant
> + * set the bandwidth replenishment timer to the replenishment instant
>   * and try to activate it.
>   *
>   * Notice that it is important for the caller to know if the timer
> @@ -530,7 +535,7 @@ static int start_dl_timer(struct task_struct *p)
>  	 * that it is actually coming from rq->clock and not from
>  	 * hrtimer's time base reading.
>  	 */
> -	act = ns_to_ktime(dl_se->deadline);
> +	act = ns_to_ktime(dl_next_period(dl_se));

Looks like there is a real bug in the code, and your fix looks correct
to me. I think it should be committed.


			Thanks,
				Luca


>  	now = hrtimer_cb_get_time(timer);
>  	delta = ktime_to_ns(now) - rq_clock(rq);
>  	act = ktime_add_ns(act, delta);