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

From: Eric Wong
Date: Mon Mar 11 2013 - 15:35:46 EST

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...

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