From: Soheil Hassas Yeganeh <soheil@xxxxxxxxxx> Subject: 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/20201106231635.3528496-6-soheil.kdev@xxxxxxxxx Signed-off-by: Soheil Hassas Yeganeh <soheil@xxxxxxxxxx> Reviewed-by: Eric Dumazet <edumazet@xxxxxxxxxx> Reviewed-by: Willem de Bruijn <willemb@xxxxxxxxxx> Reviewed-by: Khazhismel Kumykov <khazhy@xxxxxxxxxx> Cc: Guantao Liu <guantaol@xxxxxxxxxx> Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- fs/eventpoll.c | 40 +++++++++++++++++----------------------- 1 file changed, 17 insertions(+), 23 deletions(-) --- a/fs/eventpoll.c~epoll-simplify-and-optimize-busy-loop-logic +++ a/fs/eventpoll.c @@ -389,19 +389,24 @@ static bool ep_busy_loop_end(void *p, un * * 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 #else -static inline void ep_busy_loop(struct eventpoll *ep, int nonblock) -{ -} - -static inline void ep_reset_busy_poll_napi_id(struct eventpoll *ep) +static inline bool ep_busy_loop(struct eventpoll *ep, int nonblock) { + 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, } 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; _
