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

[Eric Wong <normalperson@yhbt.net>]

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