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authorShawn Bohrer <shawn.bohrer@gmail.com>2011-03-22 16:34:47 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2011-03-22 17:44:15 -0700
commitf4d93ad74c18143abd3067ca3c8ffba7d00addf4 (patch)
tree470d7e53e696c9ff2f8e62caabb50e365ac9ca8c /fs/eventpoll.c
parent3fb0e584a68cd1c5085e69be441f2ad032aaee72 (diff)
downloadlinux-f4d93ad74c18143abd3067ca3c8ffba7d00addf4.tar.gz
epoll: fix compiler warning and optimize the non-blocking path
Add a comment to ep_poll(), rename labels a bit clearly, fix a warning of unused variable from gcc and optimize the non-blocking path a little. Hinted-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Davide Libenzi <davidel@xmailserver.org> hannes@cmpxchg.org: : The non-blocking ep_poll path optimization introduced skipping over the : return value setup. : : Initialize it properly, my userspace gets upset by epoll_wait() returning : random things. : : In addition, remove the reinitialization at the fetch_events label, the : return value is garuanteed to be zero when execution reaches there. [hannes@cmpxchg.org: fix initialization] Signed-off-by: Johannes Weiner <hannes@cmpxchg.org> 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>
Diffstat (limited to 'fs/eventpoll.c')
-rw-r--r--fs/eventpoll.c33
1 files changed, 28 insertions, 5 deletions
diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index 57298d092f5..ed38801b57a 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -1148,12 +1148,29 @@ static inline struct timespec ep_set_mstimeout(long ms)
return timespec_add_safe(now, ts);
}
+/**
+ * ep_poll - Retrieves ready events, and delivers them to the caller supplied
+ * event buffer.
+ *
+ * @ep: Pointer to the eventpoll context.
+ * @events: Pointer to the userspace buffer where the ready events should be
+ * stored.
+ * @maxevents: Size (in terms of number of events) of the caller event buffer.
+ * @timeout: Maximum timeout for the ready events fetch operation, in
+ * milliseconds. If the @timeout is zero, the function will not block,
+ * while if the @timeout is less than zero, the function will block
+ * until at least one event has been retrieved (or an error
+ * occurred).
+ *
+ * Returns: Returns the number of ready events which have been fetched, or an
+ * error code, in case of error.
+ */
static int ep_poll(struct eventpoll *ep, struct epoll_event __user *events,
int maxevents, long timeout)
{
- int res, eavail, timed_out = 0;
+ int res = 0, eavail, timed_out = 0;
unsigned long flags;
- long slack;
+ long slack = 0;
wait_queue_t wait;
ktime_t expires, *to = NULL;
@@ -1164,13 +1181,18 @@ static int ep_poll(struct eventpoll *ep, struct epoll_event __user *events,
to = &expires;
*to = timespec_to_ktime(end_time);
} else if (timeout == 0) {
+ /*
+ * Avoid the unnecessary trip to the wait queue loop, if the
+ * caller specified a non blocking operation.
+ */
timed_out = 1;
+ spin_lock_irqsave(&ep->lock, flags);
+ goto check_events;
}
-retry:
+fetch_events:
spin_lock_irqsave(&ep->lock, flags);
- res = 0;
if (!ep_events_available(ep)) {
/*
* We don't have any available event to return to the caller.
@@ -1204,6 +1226,7 @@ retry:
set_current_state(TASK_RUNNING);
}
+check_events:
/* Is it worth to try to dig for events ? */
eavail = ep_events_available(ep);
@@ -1216,7 +1239,7 @@ retry:
*/
if (!res && eavail &&
!(res = ep_send_events(ep, events, maxevents)) && !timed_out)
- goto retry;
+ goto fetch_events;
return res;
}