On Fri, 4 May 2007, Davi Arnaut wrote:
> Hi,
>
> If multiple threads are parked on epoll_wait (on a single epoll fd) and
> events become available, epoll performs a wake up of all threads of the
> poll wait list, causing a thundering herd of processes trying to grab
> the eventpoll lock.
>
> This patch addresses this by using exclusive waiters (wake one). Once
> the exclusive thread finishes transferring it's events, a new thread
> is woken if there are more events available.
>
> Makes sense?
Theorically, make sense. I said theorically because all the use
epoll_wait MT use cases I've heard of, use a single thread that does the
epoll_wait, and then dispatch to worker threads. So thundering herd is not
in the picture. OTOH, it does not hurt either.
But, that code is completely changed with the new single-pass epoll delivery
code that is in -mm. So, I'd either wait for that code to go in, or I
(or you, if you like) can make a patch against -mm.
- Davide
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