The patch titled
Subject: fs/epoll: loosen irq safety in ep_scan_ready_list()
has been added to the -mm tree. Its filename is
fs-epoll-loosen-irq-safety-in-ep_scan_ready_list.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/fs-epoll-loosen-irq-safety-in-ep_scan_ready_list.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/fs-epoll-loosen-irq-safety-in-ep_scan_ready_list.patch
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From: Davidlohr Bueso <dave@xxxxxxxxxxxx>
Subject: fs/epoll: loosen irq safety in ep_scan_ready_list()
Patch series "fs/epoll: loosen irq safety when possible".
Both patches replace saving+restoring interrupts when taking the ep->lock
(now the waitqueue lock), with just disabling local irqs. This shows
immediate performance benefits in patch 1 for an epoll workload running on
Xen. The main concern we need to have with this sort of changes in epoll
is the ep_poll_callback() which is passed to the wait queue wakeup and is
done very often under irq context, this patch does not touch this call.
Patches have been tested pretty heavily with the customer workload,
microbenchmarks, ltp testcases and two high level workloads that use epoll
under the hood: nginx and libevent benchmarks.
THis patch (of 2):
Saving and restoring interrupts in ep_scan_ready_list() is an
overkill as it is never called with interrupts disabled. Loosen
this to simply disabling local irqs such that archs where managing
irqs is expensive or virtual environments. This patch yields
some throughput improvements on a workload that is epoll intensive
running on a single Xen DomU.
1 Job 7500 --> 8800 enq/s (+17%)
2 Jobs 14000 --> 15200 enq/s (+8%)
3 Jobs 20500 --> 22300 enq/s (+8%)
4 Jobs 25000 --> 28000 enq/s (+8-12)%
Link: http://lkml.kernel.org/r/20180720172956.2883-2-dave@xxxxxxxxxxxx
Signed-off-by: Davidlohr Bueso <dbueso@xxxxxxx>
Cc: Jason Baron <jbaron@xxxxxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/eventpoll.c | 9 ++++-----
1 file changed, 4 insertions(+), 5 deletions(-)
diff -puN fs/eventpoll.c~fs-epoll-loosen-irq-safety-in-ep_scan_ready_list fs/eventpoll.c
--- a/fs/eventpoll.c~fs-epoll-loosen-irq-safety-in-ep_scan_ready_list
+++ a/fs/eventpoll.c
@@ -667,7 +667,6 @@ static __poll_t ep_scan_ready_list(struc
{
__poll_t res;
int pwake = 0;
- unsigned long flags;
struct epitem *epi, *nepi;
LIST_HEAD(txlist);
@@ -687,17 +686,17 @@ static __poll_t ep_scan_ready_list(struc
* because we want the "sproc" callback to be able to do it
* in a lockless way.
*/
- spin_lock_irqsave(&ep->wq.lock, flags);
+ spin_lock_irq(&ep->wq.lock);
list_splice_init(&ep->rdllist, &txlist);
ep->ovflist = NULL;
- spin_unlock_irqrestore(&ep->wq.lock, flags);
+ spin_unlock_irq(&ep->wq.lock);
/*
* Now call the callback function.
*/
res = (*sproc)(ep, &txlist, priv);
- spin_lock_irqsave(&ep->wq.lock, flags);
+ spin_lock_irq(&ep->wq.lock);
/*
* During the time we spent inside the "sproc" callback, some
* other events might have been queued by the poll callback.
@@ -739,7 +738,7 @@ static __poll_t ep_scan_ready_list(struc
if (waitqueue_active(&ep->poll_wait))
pwake++;
}
- spin_unlock_irqrestore(&ep->wq.lock, flags);
+ spin_unlock_irq(&ep->wq.lock);
if (!ep_locked)
mutex_unlock(&ep->mtx);
_
Patches currently in -mm which might be from dave@xxxxxxxxxxxx are
ipc-sem-prevent-queuestatus-tearing-in-semop.patch
fs-epoll-loosen-irq-safety-in-ep_scan_ready_list.patch
fs-epoll-loosen-irq-safety-in-epoll_insert-and-epoll_remove.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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