From: Davidlohr Bueso <dave@xxxxxxxxxxxx> Subject: fs/epoll: avoid barrier after an epoll_wait(2) timeout Upon timeout, we can just exit out of the loop, without the cost of the changing the task's state with an smp_store_mb call. Just exit out of the loop and be done - setting the task state afterwards will be, of course, redundant. [dave@xxxxxxxxxxxx: forgotten fixlets] Link: http://lkml.kernel.org/r/20181109155258.jxcr4t2pnz6zqct3@linux-r8p5 Link: http://lkml.kernel.org/r/20181108051006.18751-7-dave@xxxxxxxxxxxx Signed-off-by: Davidlohr Bueso <dave@xxxxxxxxxxxx> Reviewed-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx> Cc: Davidlohr Bueso <dbueso@xxxxxxx> Cc: Jason Baron <jbaron@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- fs/eventpoll.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) --- a/fs/eventpoll.c~fs-epoll-avoid-barrier-after-an-epoll_wait2-timeout +++ a/fs/eventpoll.c @@ -1820,15 +1820,19 @@ fetch_events: res = -EINTR; break; } - if (ep_events_available(ep) || timed_out) + + eavail = ep_events_available(ep); + if (eavail) break; if (signal_pending(current)) { res = -EINTR; break; } - if (!schedule_hrtimeout_range(to, slack, HRTIMER_MODE_ABS)) + if (!schedule_hrtimeout_range(to, slack, HRTIMER_MODE_ABS)) { timed_out = 1; + break; + } } __set_current_state(TASK_RUNNING); _
