linux-kernel - [PATCH] sched: drop all load weight manipulation for RT tasks

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Date:	Mon, 11 Oct 2010 16:36:51 +0200
From:	Linus Walleij <linus.walleij@...ricsson.com>
To:	Ingo Molnar <mingo@...e.hu>, Peter Zijlstra <peterz@...radead.org>,
	linux-kernel@...r.kernel.org
Cc:	Linus Walleij <linus.walleij@...ricsson.com>,
	Lennart Poettering <lennart@...ttering.net>, stable@...nel.org
Subject: [PATCH] sched: drop all load weight manipulation for RT tasks

Load weights are for the CFS, they do not belong in the RT
task. This makes all RT scheduling classes leave the
CFS weights alone.

This fixes a real bug as well: I noticed the following
phonomena: a process elevated to SCHED_RR forks with
SCHED_RESET_ON_FORK set, and the child is indeed SCHED_OTHER,
and the niceval is indeed reset to 0. However the
weight inserted by set_load_weight() remains at 0. giving the
task insignificat priority.

With this fix, the weight is reset to what the task had before
being elevated to SCHED_RR/SCHED_FIFO.

Cc: Lennart Poettering <lennart@...ttering.net>
Cc: stable@...nel.org
Signed-off-by: Linus Walleij <linus.walleij@...ricsson.com>
---
Note: in 2.6.34 and earlier kernels, the phenomenon is the
inverse: the tasks return from SCHED_RR/SCHED_FIFO with huge
weights. For the stable series the earlier patch inserting
recalculation of load weights at SCHED_RESET_ON_FORK is likely
more desirable.
---
 kernel/sched.c |    6 ------
 1 files changed, 0 insertions(+), 6 deletions(-)

diff --git a/kernel/sched.c b/kernel/sched.c
index a04b8e6..07f39b5 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -1855,12 +1855,6 @@ static void dec_nr_running(struct rq *rq)
 
 static void set_load_weight(struct task_struct *p)
 {
-	if (task_has_rt_policy(p)) {
-		p->se.load.weight = 0;
-		p->se.load.inv_weight = WMULT_CONST;
-		return;
-	}
-
 	/*
 	 * SCHED_IDLE tasks get minimal weight:
 	 */
-- 
1.7.2.3

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