[lkml]   [2015]   [Feb]   [9]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: [PATCH 2/2] epoll: introduce EPOLLEXCLUSIVE and EPOLLROUNDROBIN
On 02/09/2015 12:06 PM, Jason Baron wrote:
> Epoll file descriptors that are added to a shared wakeup source are always
> added in a non-exclusive manner. That means that when we have multiple epoll
> fds attached to a shared wakeup source they are all woken up. This can
> lead to excessive cpu usage and uneven load distribution.
> This patch introduces two new 'events' flags that are intended to be used
> with EPOLL_CTL_ADD operations. EPOLLEXCLUSIVE, adds the epoll fd to the event
> source in an exclusive manner such that the minimum number of threads are
> woken. EPOLLROUNDROBIN, which depends on EPOLLEXCLUSIVE also being set, can
> also be added to the 'events' flag, such that we round robin around the set
> of waiting threads.
> An implementation note is that in the epoll wakeup routine,
> 'ep_poll_callback()', if EPOLLROUNDROBIN is set, we return 1, for a successful
> wakeup, only when there are current waiters. The idea is to use this additional
> heuristic in order minimize wakeup latencies.

I don't understand what this is intended to do.

If an event has EPOLLONESHOT, then this only one thread should be woken
regardless, right? If not, isn't that just a bug that should be fixed?

If an event has EPOLLET, then the considerations are similar to

If an event is a normal level-triggered non-one-shot event, then I don't
understand how a round-robin wakeup makes any sense. It's
level-triggered, after all.


 \ /
  Last update: 2015-02-09 21:41    [W:0.104 / U:4.188 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site