linux-kernel - [184/272] epoll: epoll_wait() should not use timespec_add

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Date:	Tue, 15 Feb 2011 16:14:01 -0800
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...nel.org
Cc:	stable-review@...nel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	Eric Dumazet <eric.dumazet@...il.com>,
	Shawn Bohrer <shawn.bohrer@...il.com>,
	Davide Libenzi <davidel@...ilserver.org>
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@...il.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@...ux-foundation.org: s/epoll_set_mstimeout/ep_set_mstimeout/, per Davide]
Reported-by: Simon Kirby <sim@...tway.ca>
Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>
Cc: Shawn Bohrer <shawn.bohrer@...il.com>
Acked-by: Davide Libenzi <davidel@...ilserver.org>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.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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