[PATCH v3] fs/epoll: Enable non-blocking busypoll when epoll timeout is 0
From: Sridhar Samudrala <sridhar.samudrala@intel.com>
Date: 2020-07-10 04:51:53
Also in:
linux-fsdevel
Subsystem:
filesystems (vfs and infrastructure), the rest · Maintainers:
Alexander Viro, Christian Brauner, Linus Torvalds
Trigger non-blocking busy poll when busy_poll is enabled and epoll is called with a timeout of 0 and is associated with a napi_id. This enables an app thread to go through napi poll routine once by calling epoll with a 0 timeout. poll/select with a 0 timeout behave in a similar manner. Signed-off-by: Sridhar Samudrala <sridhar.samudrala@intel.com> v3: reset napi_id if no event available after busy poll (Alex) v2: Added net_busy_loop_on() check (Eric) --- fs/eventpoll.c | 16 ++++++++++++++++ 1 file changed, 16 insertions(+)
diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index 12eebcdea9c8..b035b5cd19ce 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c@@ -1847,6 +1847,22 @@ static int ep_poll(struct eventpoll *ep, struct epoll_event __user *events, eavail = ep_events_available(ep); write_unlock_irq(&ep->lock); + /* + * Trigger non-blocking busy poll if timeout is 0 and there are + * no events available. Passing timed_out(1) to ep_busy_loop + * will make sure that busy polling is triggered only once. + */ + if (!eavail && net_busy_loop_on()) { + ep_busy_loop(ep, timed_out); + + write_lock_irq(&ep->lock); + eavail = ep_events_available(ep); + write_unlock_irq(&ep->lock); + + if (!evail) + ep_reset_busy_poll_napi_id(ep); + } + goto send_events; }