lkml.org 
[lkml]   [2006]   [Apr]   [26]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: accept()ing socket connections with level triggered epoll
Hello,

On Wed, Apr 26, 2006 at 02:55:57PM -0600, kyle@pbx.org wrote:
> Hello,
>
> I think I may have found a bug in Linux's implementation of epoll. My
> program creates a server socket that listens for incoming SOCK_STREAM
> connections. It uses epoll to wait for notification of a new connection
> (and also to handle the client sockets). While the client sockets use edge
> triggered epoll, for performance reasons, the server socket uses level
> triggered epoll.
>
> I have found that when I open connections to my program very quickly, it is
> sometimes possible to call accept more than once before reaching the point
> where no more connections are available and EAGAIN is returned. If I return
> to epoll_wait without accepting all of the available connections, I should
> immediately be notified that a read is still available on the server socket,
> since I am using level triggered epoll for that descriptor (at least that is
> my understanding of how all of this is supposed to work ;). However, epoll
> does not make this notification. Even if the program accepts further
> incoming connections, the missed connection is never accepted, and
> eventually times out on the client side.

I find this very strange because if your program accepts other connections,
I don't see how it could "select" some connections and ignore others. The
accept() call returns the next connection(s) in the listen queue. Stupid
question : are you sure that you don't miss anything in the loop around
accept() ? eg: reinitialise one error code or anything which could prevent
accept() from being further called after you have successfully done several
accept() at once ? I'm personnally using epoll in level triggered mode
in haproxy, which often does multiple accept() per call on very high loads
(>10k sessions/s), and although I've encountered difficult beginnings with
epoll, it's rock solid now.

> Kernel version is 2.6.9. I can provide test code if needed.

I would suggest trying 2.6.16 first to see if it may be related to a bug
which has been fixed since then, and otherwise, some test code would help.

> Thanks,
> Kyle Cronan
> <kyle@pbx.org>

Cheers,
Willy

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

\
 
 \ /
  Last update: 2006-04-26 23:23    [W:0.052 / U:1.108 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site