Similar to other calls, ep_poll() is not called with interrupts
disabled, and we can therefore avoid the irq save/restore dance
and just disable local irqs. In fact, the call should never be
called in irq context at all, considering that the only path is
epoll_wait(2) -> do_epoll_wait() -> ep_poll().
When running on a 2 socket 40-core (ht) IvyBridge a common pipe
based epoll_wait(2) microbenchmark, the following performance
improvements are seen:
# threads vanilla dirty
1 1805587 2106412
2 1854064 2090762
4 1805484 2017436
8 1751222 1974475
16 1725299 1962104
32 1378463 1571233
64 787368 900784
Which is a pretty constantly near 15%.
Also add a lockdep check such that we detect any mischief
before deadlocking.
Signed-off-by: Davidlohr Bueso <dbu...@suse.de>
---
fs/eventpoll.c | 13 +++++++------
1 file changed, 7 insertions(+), 6 deletions(-)
diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index b5e43e11f1e3..88473e6271ef 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -1746,11 +1746,12 @@ static int ep_poll(struct eventpoll *ep, struct
epoll_event __user *events,
int maxevents, long timeout)
{
int res = 0, eavail, timed_out = 0;
- unsigned long flags;
u64 slack = 0;
wait_queue_entry_t wait;
ktime_t expires, *to = NULL;
+ lockdep_assert_irqs_enabled();
+
if (timeout > 0) {
struct timespec64 end_time = ep_set_mstimeout(timeout);
@@ -1763,7 +1764,7 @@ static int ep_poll(struct eventpoll *ep, struct
epoll_event __user *events,
* caller specified a non blocking operation.
*/
timed_out = 1;
- spin_lock_irqsave(&ep->wq.lock, flags);
+ spin_lock_irq(&ep->wq.lock);
goto check_events;
}
@@ -1772,7 +1773,7 @@ static int ep_poll(struct eventpoll *ep, struct
epoll_event __user *events,
if (!ep_events_available(ep))
ep_busy_loop(ep, timed_out);
- spin_lock_irqsave(&ep->wq.lock, flags);
+ spin_lock_irq(&ep->wq.lock);
if (!ep_events_available(ep)) {
/*
@@ -1814,11 +1815,11 @@ static int ep_poll(struct eventpoll *ep, struct
epoll_event __user *events,
break;
}
- spin_unlock_irqrestore(&ep->wq.lock, flags);
+ spin_unlock_irq(&ep->wq.lock);
if (!schedule_hrtimeout_range(to, slack,
HRTIMER_MODE_ABS))
timed_out = 1;
- spin_lock_irqsave(&ep->wq.lock, flags);
+ spin_lock_irq(&ep->wq.lock);
}
__remove_wait_queue(&ep->wq, &wait);
@@ -1828,7 +1829,7 @@ static int ep_poll(struct eventpoll *ep, struct
epoll_event __user *events,
/* Is it worth to try to dig for events ? */
eavail = ep_events_available(ep);
- spin_unlock_irqrestore(&ep->wq.lock, flags);
+ spin_unlock_irq(&ep->wq.lock);
/*
* Try to transfer events to user space. In case we get 0 events and
--
2.16.4
