Re: [PATCH v2 0/2] Add epoll round robin wakeup mode

On Tue, Feb 17, 2015 at 11:33 AM, Jason Baron [off-list ref] wrote:

When we are sharing a wakeup source among multiple epoll fds, we end up with
thundering herd wakeups, since there is currently no way to add to the
wakeup source exclusively. This series introduces 2 new epoll flags,
EPOLLEXCLUSIVE for adding to a wakeup source exclusively. And EPOLLROUNDROBIN
which is to be used in conjunction to EPOLLEXCLUSIVE to evenly
distribute the wakeups. This patch was originally motivated by a desire to
improve wakeup balance and cpu usage for a listen socket() shared amongst
multiple epoll fd sets.

See: http://lwn.net/Articles/632590/ for previous test program and testing
resutls.

Epoll manpage text:

EPOLLEXCLUSIVE
        Provides exclusive wakeups when attaching multiple epoll fds to a
        shared wakeup source. Must be specified with an EPOLL_CTL_ADD operation.

EPOLLROUNDROBIN
        Provides balancing for exclusive wakeups when attaching multiple epoll
        fds to a shared wakeup soruce. Depends on EPOLLEXCLUSIVE being set and
        must be specified with an EPOLL_CTL_ADD operation.

Thanks,

What permissions do you need on the file descriptor to do this?  This
will be the first case where a poll-like operation has side effects,
and that's rather weird IMO.

--Andy

-Jason


Jason Baron (2):
  sched/wait: add round robin wakeup mode
  epoll: introduce EPOLLEXCLUSIVE and EPOLLROUNDROBIN

 fs/eventpoll.c                 | 25 ++++++++++++++++++++-----
 include/linux/wait.h           | 11 +++++++++++
 include/uapi/linux/eventpoll.h |  6 ++++++
 kernel/sched/wait.c            | 10 ++++++++--
 4 files changed, 45 insertions(+), 7 deletions(-)

--
1.8.2.rc2

--
To unsubscribe from this list: send the line "unsubscribe linux-api" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html

-- 
Andy Lutomirski
AMA Capital Management, LLC