linux-kernel - Re: [sched] redundant reschedule when set_user_nice() boosts a prio of a task from the "expired" array

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Date:	Wed, 4 Apr 2007 16:15:46 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Dmitry Adamushko <dmitry.adamushko@...il.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: [sched] redundant reschedule when set_user_nice() boosts a prio of a task from the "expired" array


* Dmitry Adamushko <dmitry.adamushko@...il.com> wrote:

> Hello,
> 
> Scenario:
> 
> Currently running [task1] boosts a priority (lowers a static_prio) of 
> [task2] via { setpriority -> set_user_nice } and [task2] happens to be 
> in the "expired" array at the moment.
> 
> According to the set_user_nice(), "delta" is negative (the prio is 
> boosted) and, hence, resched_task(rq->curr) is called.
> 
> As the [task2] is in the "expired" array and there are still tasks (at 
> least [task1]) in the "active" one, the triggered reschedule is just 
> useless (e.g. gets control back to [task1]).
> 
> Am I missing something?
> 
> The same is applicable to rt_mutex_setprio().
> 
> Of course, not a big deal, but it's easily avoidable, e.g. (delta < 0 
> && array == rq->active).

i think you are right and a micro-optimization could be done here. Would 
you like to do a patch for this?

	Ingo
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