linux-kernel - Re: Question : sched_rt.c : Loss of stats?? requeue_task_rt() does not call update_curr

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Date:	Thu, 9 Aug 2007 10:24:21 +0200
From:	"Dmitry Adamushko" <dmitry.adamushko@...il.com>
To:	"Mitchell Erblich" <erblichs@...thlink.net>
Cc:	mingo@...e.hu, linux-kernel@...r.kernel.org
Subject: Re: Question : sched_rt.c : Loss of stats?? requeue_task_rt() does not call update_curr_rt() which updates stats

On 09/08/07, Mitchell Erblich <erblichs@...thlink.net> wrote:
> sched_rt.c : requeue_task_rt()
>
> The comment states the problem requeue no dequeue.
> Put task to the end of the run list without the overhead of dequeue
> followed by enqueue.
>
> dequeue_task_rt() updates stats. Where without calling
> it will skip the stat update.
>
> Thus, shouldn't  requeue_task_rt() call
>   update_curr_rt(rq); ???

No. As update_curr_rt() suggests it's only about collecting runtime
statistics, namely
(a) the longest interval of time a given task was consuming a CPU
(i.e. == 'current') and
(b) the total amount of time it was running.

To this goal, it would be enough to call it only in
put_prev_task_rt().. I recall, we do it in dequeue_task_rt() to catch
a case of SCHED_RR/FIFO --> SCHED_NORMAL transition (e.g. in
sched_setscheduler()).. so that may make accounting a bit less precise
for (a).

-- 
Best regards,
Dmitry Adamushko
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