Re: [PATCH Resend] epoll: add EPOLLEXCLUSIVE support

[Jason Baron <jbaron@redhat.com>]

On Wed, Mar 28, 2012 at 04:09:24PM +0200, richard -rw- weinberger wrote:
> On Wed, Mar 28, 2012 at 3:57 PM, Hagen Paul Pfeifer <hagen@jauu.net> wrote:
> > High performance server sometimes create one listening socket (e.g. port
> > 80), create a epoll file descriptor and add the socket. Afterwards
> > create SC_NPROCESSORS_ONLN threads and wait for events. This often
> > result in a thundering herd problem because all CPUs are scheduled.
> >
> > This patch add an additional flag to epoll_ctl(2) called EPOLLEXCLUSIVE.
> > If a descriptor is added with this flag only one CPU is scheduled in.
> >
> > Signed-off-by: Hagen Paul Pfeifer <hagen@jauu.net>
> > ---
> > Dave rejected the patch and said not network specific. Because there
> > is no epoll maintainer this time directly.
> 
> CC'ing maintainers for you...
> Please use scripts/get_maintainer.pl.
> 

Hmmm...Looking at ep_poll() it does an '__add_wait_queue_exclusive()'.
So, I *think* epoll_wait() should do what you want, if you are waiting
on the same epfd in all the threads.

I think the case you are describing is where each thread does its own
ep_create(), and then a subsequent epoll_wait() on the fd from the
create?

So, I *think* you can get what you want without adding this flag.

Thanks,

-Jason