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Subject[184/272] epoll: epoll_wait() should not use timespec_add_ns()
2.6.37-stable review patch.  If anyone has any objections, please let us know.

------------------

From: Eric Dumazet <eric.dumazet@gmail.com>

commit 0781b909b5586f4db720b5d1838b78f9d8e42f14 upstream.

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.

[akpm@linux-foundation.org: s/epoll_set_mstimeout/ep_set_mstimeout/, per Davide]
Reported-by: Simon Kirby <sim@hostway.ca>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Shawn Bohrer <shawn.bohrer@gmail.com>
Acked-by: Davide Libenzi <davidel@xmailserver.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
fs/eventpoll.c | 16 +++++++++++++---
1 file changed, 13 insertions(+), 3 deletions(-)

--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -1111,6 +1111,17 @@ static int ep_send_events(struct eventpo
return ep_scan_ready_list(ep, ep_send_events_proc, &esed);
}

+static inline struct timespec ep_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)
{
@@ -1118,12 +1129,11 @@ static int ep_poll(struct eventpoll *ep,
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 = ep_set_mstimeout(timeout);
+
slack = select_estimate_accuracy(&end_time);
to = &expires;
*to = timespec_to_ktime(end_time);



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