On Tue, 1 Oct 2013 17:08:14 +0000 (GMT) Jason Baron <jbaron@xxxxxxxxxx> wrote:
> When calling EPOLL_CTL_ADD for an epoll file descriptor that is attached
> directly to a wakeup source, we do not need to take the global 'epmutex',
> unless the epoll file descriptor is nested. The purpose of taking
> the 'epmutex' on add is to prevent complex topologies such as loops and
> deep wakeup paths from forming in parallel through multiple EPOLL_CTL_ADD
> operations. However, for the simple case of an epoll file descriptor
> attached directly to a wakeup source (with no nesting), we do not need
> to hold the 'epmutex'.
>
> This patch along with 'epoll: optimize EPOLL_CTL_DEL using rcu' improves
> scalability on larger systems. Quoting Nathan Zimmer's mail on SPECjbb
> performance:
>
> "
> On the 16 socket run the performance went from 35k jOPS to 125k jOPS.
> In addition the benchmark when from scaling well on 10 sockets to scaling well
> on just over 40 sockets.
>
> ...
>
> Currently the benchmark stops scaling at around 40-44 sockets but it seems like
> I found a second unrelated bottleneck.
> "
I couldn't resist fiddling. Please review:
From: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Subject: epoll-do-not-take-global-epmutex-for-simple-topologies-fix
- use `bool' for boolean variables
- remove unneeded/undesirable cast of void*
- add missed ep_scan_ready_list() kerneldoc
Cc: "Paul E. McKenney" <paulmck@xxxxxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Davide Libenzi <davidel@xxxxxxxxxxxxxxx>
Cc: Eric Wong <normalperson@xxxxxxxx>
Cc: Jason Baron <jbaron@xxxxxxxxxx>
Cc: Nathan Zimmer <nzimmer@xxxxxxx>
Cc: Nelson Elhage <nelhage@xxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/eventpoll.c | 11 ++++++-----
1 file changed, 6 insertions(+), 5 deletions(-)
diff -puN fs/eventpoll.c~epoll-do-not-take-global-epmutex-for-simple-topologies-fix fs/eventpoll.c
--- a/fs/eventpoll.c~epoll-do-not-take-global-epmutex-for-simple-topologies-fix
+++ a/fs/eventpoll.c
@@ -589,13 +589,14 @@ static inline void ep_pm_stay_awake_rcu(
* @sproc: Pointer to the scan callback.
* @priv: Private opaque data passed to the @sproc callback.
* @depth: The current depth of recursive f_op->poll calls.
+ * @ep_locked: caller already holds ep->mtx
*
* Returns: The same integer error code returned by the @sproc callback.
*/
static int ep_scan_ready_list(struct eventpoll *ep,
int (*sproc)(struct eventpoll *,
struct list_head *, void *),
- void *priv, int depth, int ep_locked)
+ void *priv, int depth, bool ep_locked)
{
int error, pwake = 0;
unsigned long flags;
@@ -836,12 +837,12 @@ static void ep_ptable_queue_proc(struct
struct readyevents_arg {
struct eventpoll *ep;
- int locked;
+ bool locked;
};
static int ep_poll_readyevents_proc(void *priv, void *cookie, int call_nests)
{
- struct readyevents_arg *arg = (struct readyevents_arg *)priv;
+ struct readyevents_arg *arg = priv;
return ep_scan_ready_list(arg->ep, ep_read_events_proc, NULL,
call_nests + 1, arg->locked);
@@ -857,7 +858,7 @@ static unsigned int ep_eventpoll_poll(st
* During ep_insert() we already hold the ep->mtx for the tfile.
* Prevent re-aquisition.
*/
- arg.locked = ((wait && (wait->_qproc == ep_ptable_queue_proc)) ? 1 : 0);
+ arg.locked = wait && (wait->_qproc == ep_ptable_queue_proc);
arg.ep = ep;
/* Insert inside our poll wait queue */
@@ -1563,7 +1564,7 @@ static int ep_send_events(struct eventpo
esed.maxevents = maxevents;
esed.events = events;
- return ep_scan_ready_list(ep, ep_send_events_proc, &esed, 0, 0);
+ return ep_scan_ready_list(ep, ep_send_events_proc, &esed, 0, false);
}
static inline struct timespec ep_set_mstimeout(long ms)
_
--
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