linux-kernel - wfcqueue (in Userspace RCU) for Linux kernel (for epoll)

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Message-ID: <20130311193541.GA11149@dcvr.yhbt.net>
Date:	Mon, 11 Mar 2013 19:35:41 +0000
From:	Eric Wong <normalperson@...t.net>
To:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Lai Jiangshan <laijs@...fujitsu.com>
Cc:	linux-kernel@...r.kernel.org,
	Davide Libenzi <davidel@...ilserver.org>
Subject: wfcqueue (in Userspace RCU) for Linux kernel (for epoll)

Hi, I'm looking to reduce contention for the ep->lock spin lock in epoll.

I came across wfcqueue in Userspace RCU and am wondering if there's any
reason (other that lack of developer time/users) it hasn't been adapted
for the Linux kernel.

I'd be happy to do the work if it's suitable (and omit parts which
may not be, such as busy wait).

Using a mutex lock (while in process context) for dequeue works for
epoll.  I mainly want a lock-free enqueue for ep_poll_callback since
that may be called in IRQ context.

I suppose I can also use the llist LIFO in ep_poll_callback and
reverse that while in process context, too...

ref: http://git.lttng.org/userspace-rcu.git
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