From mboxrd@z Thu Jan  1 00:00:00 1970
From: David Howells <dhowells@redhat.com>
Subject: Re: [RFC] sched: implement the exclusive wait queue as a LIFO queue
Date: Wed, 28 Apr 2010 14:21:02 +0100
Message-ID: <12671.1272460862@redhat.com>
References: <q2m412e6f7f1004280417h449c67f9g86fca3dbece106e3@mail.gmail.com> <1272430986-20436-1-git-send-email-xiaosuo@gmail.com> <u2w7b6bb4a51004280047s8748cbfbi7ed8e2a238121fa9@mail.gmail.com> <q2j412e6f7f1004280052ice434710ra17a4516236bd3f3@mail.gmail.com> <20100428081545.GA19027@windriver.com> <u2t412e6f7f1004280123k642a1511gbce3ed784431dc1d@mail.gmail.com> <8482.1272446987@redhat.com>
Cc: dhowells@redhat.com, Yong Zhang <yong.zhang@windriver.com>,
	Xiaotian Feng <xtfeng@gmail.com>, Ingo Molnar <mingo@elte.hu>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	Andrew Morton <akpm@linux-foundation.org>,
	"Eric W. Biederman" <ebiederm@xmission.com>,
	Davide Libenzi <davidel@xmailserver.org>,
	Roland Dreier <rolandd@cisco.com>,
	Stefan Richter <stefanr@s5r6.in-berlin.de>,
	Peter Zijlstra <a.p.zijlstra@chello.nl>,
	"David S. Miller" <davem@davemloft.net>,
	Eric Dumazet <dada1@cosmosbay.com>,
	Christoph Lameter <cl@linux.com>,
	Andreas Herrmann <andreas.herrmann3@amd.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Takashi Iwai <tiwai@suse.de>, linux-fsdevel@vger.kernel.org,
	linux-kernel@vger.kernel.org
To: Changli Gao <xiaosuo@gmail.com>
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Changli Gao <xiaosuo@gmail.com> wrote:

> You are right. I made the wrong assumption. But we indeed need some
> primitive to add wait_queue at the head of the wait_queue_head, and I
> know epoll needs it, at least.
> 
> fs/eventpoll.c: 1443.
>                 wait.flags |= WQ_FLAG_EXCLUSIVE;
>                 __add_wait_queue(&ep->wq, &wait);

You can add at either end of the wait queue with __add_wait_queue() and
__add_wait_queue_tail().

David