Jason Baron <jbaron@xxxxxxxxxx> wrote:
> epoll: reduce usage of global 'epmutex' lock
>
> Epoll file descriptors that are 1 link from a wakeup source and
> are not nested within other epoll descriptors, or pointing to
> other epoll descriptors, don't need to check for loop creation or
> the creation of wakeup storms. Because of this we can avoid taking
> the global 'epmutex' in these cases. This state for the epoll file
> descriptor is marked as 'EVENTPOLL_BASIC'. Once the epoll file
> descriptor is attached to another epoll file descriptor it is
> labeled as 'EVENTPOLL_COMPLEX', and full loop checking and wakeup
> storm creation are checked using the the global 'epmutex'. It does
> not transition back. Hopefully, this is a common usecase...
Cool. I was thinking about doing the same thing down the line (for
EPOLL_CTL_ADD, too)
> @@ -166,6 +167,14 @@ struct epitem {
>
> /* The structure that describe the interested events and the source fd */
> struct epoll_event event;
> +
> + /* TODO: really necessary? */
> + int on_list;
There's some things we can overload to avoid increasing epitem size
(.ep, .ffd.fd, ...), so on_list should be unnecessary.
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