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Commit 95aac7b1 authored by Shawn Bohrer's avatar Shawn Bohrer Committed by Linus Torvalds
Browse files

epoll: make epoll_wait() use the hrtimer range feature 



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: default avatarShawn Bohrer <shawn.bohrer@gmail.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Acked-by: default avatarDavide Libenzi <davidel@xmailserver.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 231f3d39

fs/eventpoll.c

+19 −16
Original line number Diff line number Diff line
@@ -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)
@@ -1117,18 +1114,22 @@ 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;

	struct timespec end_time;

	ktime_t expires, *to = NULL;



	/*

	 * 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;

	if (timeout > 0) {

		ktime_get_ts(&end_time);

		timespec_add_ns(&end_time, (u64)timeout * NSEC_PER_MSEC);

		slack = select_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);
@@ -1150,7 +1151,7 @@ static int ep_poll(struct eventpoll *ep, struct epoll_event __user *events, 
			 * 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;
@@ -1158,7 +1159,9 @@ static int ep_poll(struct eventpoll *ep, struct epoll_event __user *events, 
			}



			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);
@@ -1176,7 +1179,7 @@ static int ep_poll(struct eventpoll *ep, struct epoll_event __user *events, 
	 * 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;

fs/select.c

+1 −1
Original line number Diff line number Diff line
@@ -67,7 +67,7 @@ static long __estimate_accuracy(struct timespec *tv) 
	return slack;

}



static long select_estimate_accuracy(struct timespec *tv)

long select_estimate_accuracy(struct timespec *tv)

{

	unsigned long ret;

	struct timespec now;

include/linux/poll.h

+2 −0
Original line number Diff line number Diff line
@@ -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 select_estimate_accuracy(struct timespec *tv);





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

{