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

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Message-ID: <6096.1272463619@redhat.com>
Date:	Wed, 28 Apr 2010 15:06:59 +0100
From:	David Howells <dhowells@...hat.com>
To:	Changli Gao <xiaosuo@...il.com>
Cc:	dhowells@...hat.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>,
	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

Changli Gao <xiaosuo@...il.com> wrote:

> I don't know how to do that, as maybe there are non-exclusive and
> exclusive wait queues in the same wait queue head. If we want to
> enqueue exclusive wait queues at the head of exclusive queues, we have
> to know where the head is, otherwise, we have to loop to find the head
> when enqueuing.

I suspect you really want to have the semantics defined per-queue.  _Either_ a
queue is FIFO (such as processes waiting for a resource so they can do
something with it) _or_ it is LIFO (such as a pool of processes waiting to be
given work).

How often do the two actually mix?  And if they do, is that really an error?

David
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