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From: Nikita Danilov <nikita@clusterfs.com>
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Date: Tue, 2 Nov 2004 18:16:30 +0300
To: Nick Piggin <nickpiggin@yahoo.com.au>
Cc: Con Kolivas <kernel@kolivas.org>, linux <linux-kernel@vger.kernel.org>,
       Andrew Morton <akpm@osdl.org>, Ingo Molnar <mingo@elte.hu>
Subject: Re: [PATCH] add requeue task
In-Reply-To: <41877F2D.6070200@yahoo.com.au>
References: <418707E5.90705@kolivas.org>
	<41877F2D.6070200@yahoo.com.au>
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Nick Piggin writes:
 > Con Kolivas wrote:
 > > add requeue task
 > > 
 > > 
 > > 
 > > ------------------------------------------------------------------------
 > > 
 > > We can requeue tasks for cheaper then doing a complete dequeue followed by
 > > an enqueue. Add the requeue_task function and perform it where possible.
 > > 
 > > Change the granularity code to requeue tasks at their best priority
 > > instead of changing priority while they're running. This keeps tasks at
 > > their top interactive level during their whole timeslice.
 > > 
 > 
 > I wonder... these things are all in sufficiently rarely used places,
 > that the icache miss might be more costly than the operations saved.
 > 
 > But....
 > 
 > > Signed-off-by: Con Kolivas <kernel@kolivas.org>
 > > 
 > > Index: linux-2.6.10-rc1-mm2/kernel/sched.c
 > > ===================================================================
 > > --- linux-2.6.10-rc1-mm2.orig/kernel/sched.c	2004-11-02 14:48:54.686316718 +1100
 > > +++ linux-2.6.10-rc1-mm2/kernel/sched.c	2004-11-02 14:52:51.805763544 +1100
 > > @@ -579,6 +579,16 @@ static void enqueue_task(struct task_str
 > >  }
 > >  
 > >  /*
 > > + * Put task to the end of the run list without the overhead of dequeue
 > > + * followed by enqueue.
 > > + */
 > > +static void requeue_task(struct task_struct *p, prio_array_t *array)
 > > +{
 > > +	list_del(&p->run_list);
 > > +	list_add_tail(&p->run_list, array->queue + p->prio);
 > > +}

Shouldn't this be

list_move_tail(&p->run_list, array->queue + p->prio);

?

Nikita.