The patch titled
Subject: fs/eventpoll.c: loosen irq safety in ep_poll()
has been added to the -mm tree. Its filename is
fs-epoll-loosen-irq-safety-in-ep_poll.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/fs-epoll-loosen-irq-safety-in-ep_poll.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/fs-epoll-loosen-irq-safety-in-ep_poll.patch
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------------------------------------------------------
From: Davidlohr Bueso <dave@xxxxxxxxxxxx>
Subject: fs/eventpoll.c: loosen irq safety in ep_poll()
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.
Link: http://lkml.kernel.org/r/20180727053432.16679-2-dave@xxxxxxxxxxxx
Signed-off-by: Davidlohr Bueso <dbueso@xxxxxxx>
Reviewed-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Jason Baron <jbaron@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
diff -puN fs/eventpoll.c~fs-epoll-loosen-irq-safety-in-ep_poll fs/eventpoll.c
--- a/fs/eventpoll.c~fs-epoll-loosen-irq-safety-in-ep_poll
+++ a/fs/eventpoll.c
@@ -1746,11 +1746,12 @@ static int ep_poll(struct eventpoll *ep,
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,
* 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 @@ fetch_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 @@ fetch_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 @@ check_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
_
Patches currently in -mm which might be from dave@xxxxxxxxxxxx are
fs-epoll-loosen-irq-safety-in-ep_scan_ready_list.patch
fs-epoll-loosen-irq-safety-in-epoll_insert-and-epoll_remove.patch
fs-epoll-robustify-irq-safety-with-lockdep_assert_irqs_enabled.patch
fs-epoll-simply-config_net_rx_busy_poll-ifdefery.patch
fs-epoll-loosen-irq-safety-in-ep_poll.patch
fs-eventpoll-simplify-ep_is_linked-callers.patch
ipc-drop-ipc_lock.patch
lib-rhashtable-simplify-bucket_table_alloc.patch
lib-rhashtable-guarantee-initial-hashtable-allocation.patch
ipc-get-rid-of-ids-tables_initialized-hack.patch
ipc-simplify-ipc-initialization.patch
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