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Hash : cf249e7d
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Date : 2010-07-19T13:44:56
Possible fix to 100% cpu usage with epoll and openssl I'm running a fairly simple bit of test code using libevent2 with epoll and openssl bufferevents and I've run into a 100% cpu usage problem. Looking into it 100% usage was caused by epoll_wait constantly returning write events on the openssl socket when it shouldn't really have been looking for write events at all (N_ACTIVE_CALLBACKS() was returning 0 also). Looking a bit deeper eventbuffer_openssl socket seems to be requesting that the EV_WRITE event be removed when it should, but the event isn't actually being removed from epoll. Continuing to follow this I think I've found a bug in event_changelist_del. For evpoll event_del calls event_changelist_del which caches the change which is then actioned later when evpoll_dispatch is called. In event_changlist_del there is a check so that if the currently changed action is an add then the cached action is changed to a no-op rather than a delete (which makes sense). The problem arises if there are more than two add or delete operations between calls to dispatch, in this case it's possible that the delete is turned into a no-op when it shouldn't have been. For example starting with the event on, a delete followed by an add and then another delete results in a no-op when it should have been a delete (I added a fair bit of debug output that seems to confirm this behaviour). I've applied a small change that checks the original old_event stored with the change and only converts the delete to a no-op if the event isn't on in old_event. This seems to have fixed my problem.
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0. BUILDING AND INSTALLATION (Briefly) $ ./configure $ make $ make verify # (optional) $ sudo make install 1. BUILDING AND INSTALLATION (In Depth) To build libevent, type $ ./configure && make (If you got libevent from the git repository, you will first need to run the included "autogen.sh" script in order to generate the configure script.) Install as root via # make install You can run the regression tests by running $ make verify Before, reporting any problems, please run the regression tests. To enable the low-level tracing build the library as: CFLAGS=-DUSE_DEBUG ./configure [...] Standard configure flags should work. In particular, see: --disable-shared Only build static libraries --prefix Install all files relative to this directory. The configure script also supports the following flags: --enable-gcc-warnings Enable extra compiler checking with GCC. --disable-malloc-replacement Don't let applications replace our memory management functions --disable-openssl Disable support for OpenSSL encryption. --disable-thread-support Don't support multithreaded environments. 2. USEFUL LINKS: For the latest released version of Libevent, see the official website at http://monkey.org/~provos/libevent/ . There's a pretty good work-in-progress manual up at http://www.wangafu.net/~nickm/libevent-book/ . For the latest development versions of Libevent, access our Git repository via "git clone git://levent.git.sourceforge.net/gitroot/levent/libevent" You can browse the git repository online at http://levent.git.sourceforge.net/git/gitweb-index.cgi . To report bugs, request features, or submit patches to Libevent, use the Sourceforge trackers at https://sourceforge.net/tracker/?group_id=50884 . There's also a libevent-users mailing list for talking about Libevent use and development: http://archives.seul.org/libevent/users/ 3. ACKNOWLEDGMENTS The following people have helped with suggestions, ideas, code or fixing bugs: Alejo Weston Andros Adamson William Ahern Stas Bekman Ka-Hing Cheung Andrew Danforth Christopher Davis Mike Davis Shie Erlich Alexander von Gernler Artur Grabowski Aaron Hopkins Tani Hosokawa Claudio Jeker Valery Kyholodov Marko Kreen Scott Lamb Adam Langley Christopher Layne Philip Lewis David Libenzi Moshe Litvin Hagne Mahre Lubomir Marinov Nick Mathewson James Mansion Andrey Matveev Caitlin Mercer Trond Norbye Richard Nyberg Jon Oberheide Phil Oleson Dave Pacheco Tassilo von Parseval Pierre Phaneuf Ryan Phillips Jon Poland Bert JW Regeer Hanna Schroeter Kevin Springborn Ferenc Szalai Dug Song Zack Weinberg Taral propanbutan mmadia If we have forgotten your name, please contact us.