linux-kernel - Re: [RFC] sched: implement the exclusive wait queue as a LIFO queue

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Date:	Wed, 28 Apr 2010 11:25:48 +0200
From:	Johannes Weiner <hannes@...xchg.org>
To:	Changli Gao <xiaosuo@...il.com>
Cc:	Yong Zhang <yong.zhang@...driver.com>,
	Xiaotian Feng <xtfeng@...il.com>, Ingo Molnar <mingo@...e.hu>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Davide Libenzi <davidel@...ilserver.org>,
	Roland Dreier <rolandd@...co.com>,
	Stefan Richter <stefanr@...6.in-berlin.de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <dada1@...mosbay.com>,
	Christoph Lameter <cl@...ux.com>,
	Andreas Herrmann <andreas.herrmann3@....com>,
	Thomas Gleixner <tglx@...utronix.de>,
	David Howells <dhowells@...hat.com>,
	Takashi Iwai <tiwai@...e.de>, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC] sched: implement the exclusive wait queue as a LIFO queue

On Wed, Apr 28, 2010 at 04:23:52PM +0800, Changli Gao wrote:
> On Wed, Apr 28, 2010 at 4:15 PM, Yong Zhang <yong.zhang@...driver.com> wrote:
> >
> > What do you mean "we don't need these processes"?
> 
> If the work is less than the workers, we don't need the workers at the
> tail of the exculsive list.

Have you checked how exclusive waitqueues are even used?

> > So some processs(at the tail of exclusive list)will be treated abnormally
> > and it will sleep for a long time, is this reasonable?
> >
> 
> If there isn't enough work to be done, we'd better not disrupt them
> and  leave them sleeping forever to keep the scheduler happier. Do we
> have reason to keep fair to all the workers? Does it have benefit?

How about starving lock contenders?  See wait_on_bit_lock() and grep
for the users e.g.
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