From dd2ae32bc181efdc134c25359bc67d073c48a1d0 Mon Sep 17 00:00:00 2001 From: Nick Mathewson Date: Thu, 16 Dec 2010 13:35:09 -0500 Subject: [PATCH] Turn on epoll changelists with libevent 2.0.9-rc and later Libevent 2.0 has a "changelist" feature that avoids making redundant syscalls if we wind up doing a lot of event_add/event_del operations on the same fd in a row. Unfortunately, due to a weird design choice in Linux, it doesn't work right with epoll when multiple fds refer to the same socket (e.g., one is a dup() of the other). We don't dup() anything we give to Libevent, though, so it is safe for us to explicitly turn this feature on. --- src/common/compat_libevent.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/src/common/compat_libevent.c b/src/common/compat_libevent.c index d3b9eb3afa..7bbad54415 100644 --- a/src/common/compat_libevent.c +++ b/src/common/compat_libevent.c @@ -186,6 +186,12 @@ tor_libevent_initialize(tor_libevent_cfg *torcfg) event_config_set_num_cpus_hint(cfg, torcfg->num_cpus); #endif +#if LIBEVENT_VERSION_NUMBER >= V(2,0,9) + /* We can enable changelist support with epoll, since we don't give + * Libevent any dup'd fds. This lets us avoid some syscalls. */ + event_config_set_flag(cfg, EVENT_BASE_FLAG_EPOLL_USE_CHANGELIST); +#endif + the_event_base = event_base_new_with_config(cfg); event_config_free(cfg);