Messages in this thread Patch in this message | | | Subject | Re: sys_epoll_wait high CPU load in 2.6.37 | From | Eric Dumazet <> | Date | Wed, 26 Jan 2011 19:45:37 +0100 |
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Le mercredi 26 janvier 2011 à 19:18 +0100, Eric Dumazet a écrit : > Le mercredi 26 janvier 2011 à 10:06 -0800, Davide Libenzi a écrit : > > > Eric, if you look at fs/select.c (~line 925), poll does exactly the same > > thing as epoll do. > > It too, ignores the eventual return value of poll_select_set_timeout(), so > > maybe a little bit more optimized ktime_get_ts+timespec_add_ms could make > > sense. > > > > OK, I'll post a V3 ;)
Well in the poll() case we handle a zero timeout, not in epoll().
So the helper function cannot be shared and can be static to epoll.
[PATCH v3] epoll: epoll_wait() should not use timespec_add_ns()
commit 95aac7b1cd224f (epoll: make epoll_wait() use the hrtimer range feature) added a performance regression because it uses timespec_add_ns() with potential very large 'ns' values.
Reported-by: Simon Kirby <sim@hostway.ca> Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com> CC: Shawn Bohrer <shawn.bohrer@gmail.com> CC: Davide Libenzi <davidel@xmailserver.org> CC: Thomas Gleixner <tglx@linutronix.de> CC: Andrew Morton <akpm@linux-foundation.org> --- fs/eventpoll.c | 16 +++++++++++++--- 1 file changed, 13 insertions(+), 3 deletions(-)
diff --git a/fs/eventpoll.c b/fs/eventpoll.c index cc8a9b7..d517aa3 100644 --- a/fs/eventpoll.c +++ b/fs/eventpoll.c @@ -1114,6 +1114,17 @@ static int ep_send_events(struct eventpoll *ep, return ep_scan_ready_list(ep, ep_send_events_proc, &esed); } +static inline struct timespec epoll_set_mstimeout(long ms) +{ + struct timespec now, ts = { + .tv_sec = ms / MSEC_PER_SEC, + .tv_nsec = NSEC_PER_MSEC * (ms % MSEC_PER_SEC), + }; + + ktime_get_ts(&now); + return timespec_add_safe(now, ts); +} + static int ep_poll(struct eventpoll *ep, struct epoll_event __user *events, int maxevents, long timeout) { @@ -1121,12 +1132,11 @@ static int ep_poll(struct eventpoll *ep, struct epoll_event __user *events, unsigned long flags; long slack; wait_queue_t wait; - struct timespec end_time; ktime_t expires, *to = NULL; if (timeout > 0) { - ktime_get_ts(&end_time); - timespec_add_ns(&end_time, (u64)timeout * NSEC_PER_MSEC); + struct timespec end_time = epoll_set_mstimeout(timeout); + slack = select_estimate_accuracy(&end_time); to = &expires; *to = timespec_to_ktime(end_time);
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