Messages in this thread Patch in this message | | | From | Davidlohr Bueso <> | Subject | [PATCH 1/2] fs/epoll: loosen irq safety in ep_poll() | Date | Thu, 26 Jul 2018 22:34:31 -0700 |
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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 <dbueso@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
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