linux-kernel - [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 16:04:02 +0200
From:	"Dmitry Adamushko" <dmitry.adamushko@...il.com>
To:	"Ingo Molnar" <mingo@...e.hu>
Cc:	"Andrew Morton" <akpm@...ux-foundation.org>,
	"Linux Kernel" <linux-kernel@...r.kernel.org>
Subject: [sched] redundant reschedule when set_user_nice() boosts a prio of a task from the "expired" array

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).

Thanks in advance for any comments.

-- 
Best regards,
Dmitry Adamushko
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