Re: [Libevent-users] 100% cpu utilization with openssl bufferevent.

[Nick Mathewson <nickm@xxxxxxxxxxxxx>]

On Thu, Apr 29, 2010 at 5:19 AM, Sebastian Sjöberg
<Sebastian.Sjoberg@xxxxxxxx> wrote:
> Hi,
>
> I've encountered a problem with openssl bufferevents where libevent reports fd:s as writeable but no action is being taken.

 [...]
> There is no problem when I'm connecting without tls so I think this is an issue with openssl bufferevents and my guess is that somehow the write events that openssl bufferevents sets up sometimes doesn't get removed or disabled properly.
>
> Is this an issue that someone else has seen and does anyone have any pointers on how to debug this problem?


I haven't run into this myself yet, but the openssl code is relatively
new, and probably has some bugs left.

To clarify, it seems that the problem is that Libevent bufferevent
openssl code never deletes the relevant read events, even though it
isn't actually interested in reading?  Or the problem is that epoll is
returning immediately but not making any events active?

If it's the first problem, I'd try adding debugging messages to the
points in bufferevent_openssl that call event_add, event_del, and
_bufferevent_add_event, along with debugging statements to display the
return values of SSL_read and SSL_write, to see at what point we're
supposed to be deleting the relevant read event but not really doing
it.

If it's the second problem, I'd start by testing whether stuff begins
to work when you set the EVENT_NOEPOLL environment variable.  If so,
then the bug is probably with the epoll backend -- or at least, it
requires the epoll backend to appear.  To debug this, I'd add
debugging messages to the loop in epoll_dispatch that calls
evmap_io_active to tell me whenever it decided not to call
evmap_io_active, and I'd have evmap_io_active tell me whenever it made
0 events become active.

With any luck, the debugging output should help figure out exactly
what's going wrong here.

I'm afraid I'm about to be away from the internet for tomorrow and the
weekend, so I won't be able to help much more until early next week.
Good luck!

yrs,
--
Nick
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