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Subject[PATCH] hrtimer: make epoll_wait() use the hrtimer range feature
Date
This make epoll use hrtimers for the timeout value which prevents
epoll_wait() from timing out up to a millisecond early.

This mirrors the behavior of select() and poll().

Signed-off-by: Shawn Bohrer <shawn.bohrer@gmail.com>
---
fs/eventpoll.c | 35 +++++++++++++++++++----------------
fs/select.c | 2 +-
include/linux/poll.h | 2 ++
3 files changed, 22 insertions(+), 17 deletions(-)
diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index 3817149..728f56c 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -77,9 +77,6 @@
/* Maximum number of nesting allowed inside epoll sets */
#define EP_MAX_NESTS 4

-/* Maximum msec timeout value storeable in a long int */
-#define EP_MAX_MSTIMEO min(1000ULL * MAX_SCHEDULE_TIMEOUT / HZ, (LONG_MAX - 999ULL) / HZ)
-
#define EP_MAX_EVENTS (INT_MAX / sizeof(struct epoll_event))

#define EP_UNACTIVE_PTR ((void *) -1L)
@@ -1116,18 +1113,22 @@ static int ep_send_events(struct eventpoll *ep,
static int ep_poll(struct eventpoll *ep, struct epoll_event __user *events,
int maxevents, long timeout)
{
- int res, eavail;
+ int res, eavail, timed_out = 0;
unsigned long flags;
- long jtimeout;
+ long slack;
wait_queue_t wait;
-
- /*
- * Calculate the timeout by checking for the "infinite" value (-1)
- * and the overflow condition. The passed timeout is in milliseconds,
- * that why (t * HZ) / 1000.
- */
- jtimeout = (timeout < 0 || timeout >= EP_MAX_MSTIMEO) ?
- MAX_SCHEDULE_TIMEOUT : (timeout * HZ + 999) / 1000;
+ 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);
+ slack = estimate_accuracy(&end_time);
+ to = &expires;
+ *to = timespec_to_ktime(end_time);
+ } else if (timeout == 0) {
+ timed_out = 1;
+ }

retry:
spin_lock_irqsave(&ep->lock, flags);
@@ -1149,7 +1150,7 @@ retry:
* to TASK_INTERRUPTIBLE before doing the checks.
*/
set_current_state(TASK_INTERRUPTIBLE);
- if (!list_empty(&ep->rdllist) || !jtimeout)
+ if (!list_empty(&ep->rdllist) || timed_out)
break;
if (signal_pending(current)) {
res = -EINTR;
@@ -1157,7 +1158,9 @@ retry:
}

spin_unlock_irqrestore(&ep->lock, flags);
- jtimeout = schedule_timeout(jtimeout);
+ if (!schedule_hrtimeout_range(to, slack, HRTIMER_MODE_ABS))
+ timed_out = 1;
+
spin_lock_irqsave(&ep->lock, flags);
}
__remove_wait_queue(&ep->wq, &wait);
@@ -1175,7 +1178,7 @@ retry:
* more luck.
*/
if (!res && eavail &&
- !(res = ep_send_events(ep, events, maxevents)) && jtimeout)
+ !(res = ep_send_events(ep, events, maxevents)) && !timed_out)
goto retry;

return res;
diff --git a/fs/select.c b/fs/select.c
index 500a669..003cb77 100644
--- a/fs/select.c
+++ b/fs/select.c
@@ -67,7 +67,7 @@ static long __estimate_accuracy(struct timespec *tv)
return slack;
}

-static long estimate_accuracy(struct timespec *tv)
+long estimate_accuracy(struct timespec *tv)
{
unsigned long ret;
struct timespec now;
diff --git a/include/linux/poll.h b/include/linux/poll.h
index 600cc1f..52be81f 100644
--- a/include/linux/poll.h
+++ b/include/linux/poll.h
@@ -73,6 +73,8 @@ extern void poll_initwait(struct poll_wqueues *pwq);
extern void poll_freewait(struct poll_wqueues *pwq);
extern int poll_schedule_timeout(struct poll_wqueues *pwq, int state,
ktime_t *expires, unsigned long slack);
+extern long estimate_accuracy(struct timespec *tv);
+

static inline int poll_schedule(struct poll_wqueues *pwq, int state)
{
--
1.7.2.1


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