linux-kernel - Re: [Announce] [patch] Modular Scheduler Core and Completely Fair Scheduler [CFS]

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Message-ID: <20070414063254.GB14875@elte.hu>
Date:	Sat, 14 Apr 2007 08:32:54 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Nick Piggin <npiggin@...e.de>
Cc:	linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Con Kolivas <kernel@...ivas.org>,
	Mike Galbraith <efault@....de>,
	Arjan van de Ven <arjan@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [Announce] [patch] Modular Scheduler Core and Completely Fair Scheduler [CFS]


* Nick Piggin <npiggin@...e.de> wrote:

> >    The CFS patch uses a completely different approach and implementation
> >    from RSDL/SD. My goal was to make CFS's interactivity quality exceed
> >    that of RSDL/SD, which is a high standard to meet :-) Testing
> >    feedback is welcome to decide this one way or another. [ and, in any
> >    case, all of SD's logic could be added via a kernel/sched_sd.c module
> >    as well, if Con is interested in such an approach. ]
> 
> Comment about the code: shouldn't you be requeueing the task in the 
> rbtree wherever you change wait_runtime? eg. task_new_fair? [...]

yes: the task's position within the rbtree is updated every time 
wherever wait_runtime is change. task_new_fair is the method during new 
task creation, but indeed i forgot to requeue the parent. I've fixed 
this in my tree (see the delta patch below) - thanks!

	Ingo

----------->
From: Ingo Molnar <mingo@...e.hu>
Subject: [cfs] fix parent's rbtree position

Nick noticed that upon fork we change parent->wait_runtime but we do not 
requeue it within the rbtree.

Signed-off-by: Ingo Molnar <mingo@...e.hu>

Index: linux/kernel/sched_fair.c
===================================================================
--- linux.orig/kernel/sched_fair.c
+++ linux/kernel/sched_fair.c
@@ -524,6 +524,8 @@ static void task_new_fair(struct rq *rq,
 
 	p->wait_runtime = parent->wait_runtime/2;
 	parent->wait_runtime /= 2;
+	requeue_task_fair(rq, parent);
+
 	/*
 	 * For the first timeslice we allow child threads
 	 * to move their parent-inherited fairness back
-
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