epoll: simplify and optimize busy loop logic
ep_events_available() is called multiple times around the busy loop logic,
even though the logic is generally not used. ep_reset_busy_poll_napi_id()
is similarly always called, even when busy loop is not used.
Eliminate ep_reset_busy_poll_napi_id() and inline it inside
ep_busy_loop(). Make ep_busy_loop() return whether there are any events
available after the busy loop. This will eliminate unnecessary loads and
branches, and simplifies the loop.
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Soheil Hassas Yeganeh <[email protected]>
Reviewed-by: Eric Dumazet <[email protected]>
Reviewed-by: Willem de Bruijn <[email protected]>
Reviewed-by: Khazhismel Kumykov <[email protected]>
Cc: Guantao Liu <[email protected]>
Cc: Linus Torvalds <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index d8eef215..03d0ac0 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -389,19 +389,24 @@ static bool ep_busy_loop_end(void *p, unsigned long start_time)
*
* we must do our busy polling with irqs enabled
*/
-static void ep_busy_loop(struct eventpoll *ep, int nonblock)
+static bool ep_busy_loop(struct eventpoll *ep, int nonblock)
{
unsigned int napi_id = READ_ONCE(ep->napi_id);
- if ((napi_id >= MIN_NAPI_ID) && net_busy_loop_on())
+ if ((napi_id >= MIN_NAPI_ID) && net_busy_loop_on()) {
napi_busy_loop(napi_id, nonblock ? NULL : ep_busy_loop_end, ep, false,
BUSY_POLL_BUDGET);
-}
-
-static inline void ep_reset_busy_poll_napi_id(struct eventpoll *ep)
-{
- if (ep->napi_id)
+ if (ep_events_available(ep))
+ return true;
+ /*
+ * Busy poll timed out. Drop NAPI ID for now, we can add
+ * it back in when we have moved a socket with a valid NAPI
+ * ID onto the ready list.
+ */
ep->napi_id = 0;
+ return false;
+ }
+ return false;
}
/*
@@ -441,12 +446,9 @@ static inline void ep_set_busy_poll_napi_id(struct epitem *epi)
#else
-static inline void ep_busy_loop(struct eventpoll *ep, int nonblock)
+static inline bool ep_busy_loop(struct eventpoll *ep, int nonblock)
{
-}
-
-static inline void ep_reset_busy_poll_napi_id(struct eventpoll *ep)
-{
+ return false;
}
static inline void ep_set_busy_poll_napi_id(struct epitem *epi)
@@ -1772,21 +1774,13 @@ static int ep_poll(struct eventpoll *ep, struct epoll_event __user *events,
}
fetch_events:
-
- if (!ep_events_available(ep))
- ep_busy_loop(ep, timed_out);
-
eavail = ep_events_available(ep);
+ if (!eavail)
+ eavail = ep_busy_loop(ep, timed_out);
+
if (eavail)
goto send_events;
- /*
- * Busy poll timed out. Drop NAPI ID for now, we can add
- * it back in when we have moved a socket with a valid NAPI
- * ID onto the ready list.
- */
- ep_reset_busy_poll_napi_id(ep);
-
do {
if (signal_pending(current))
return -EINTR;
