From: Davidlohr Bueso <dave@stgolabs.net>
To: akpm@linux-foundation.org
Cc: jbaron@akamai.com, viro@zeniv.linux.org.uk, dave@stgolabs.net,
linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
Davidlohr Bueso <dbueso@suse.de>
Subject: [PATCH 2/6] fs/epoll: simplify ep_send_events_proc() ready-list loop
Date: Wed, 7 Nov 2018 21:10:02 -0800 [thread overview]
Message-ID: <20181108051006.18751-3-dave@stgolabs.net> (raw)
In-Reply-To: <20181108051006.18751-1-dave@stgolabs.net>
The current logic is a bit convoluted. Lets simplify this with
a standard list_for_each_entry_safe() loop instead and just
break out after maxevents is reached.
While at it, remove an unnecessary indentation level in the loop
when there are in fact ready events.
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
---
fs/eventpoll.c | 73 +++++++++++++++++++++++++++++-----------------------------
1 file changed, 37 insertions(+), 36 deletions(-)
diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index 7ad020f1353b..101d46b81f64 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -1624,21 +1624,22 @@ static __poll_t ep_send_events_proc(struct eventpoll *ep, struct list_head *head
{
struct ep_send_events_data *esed = priv;
__poll_t revents;
- struct epitem *epi;
- struct epoll_event __user *uevent;
+ struct epitem *epi, *tmp;
+ struct epoll_event __user *uevent = esed->events;
struct wakeup_source *ws;
poll_table pt;
init_poll_funcptr(&pt, NULL);
+ esed->res = 0;
/*
* We can loop without lock because we are passed a task private list.
* Items cannot vanish during the loop because ep_scan_ready_list() is
* holding "mtx" during this call.
*/
- for (esed->res = 0, uevent = esed->events;
- !list_empty(head) && esed->res < esed->maxevents;) {
- epi = list_first_entry(head, struct epitem, rdllink);
+ list_for_each_entry_safe(epi, tmp, head, rdllink) {
+ if (esed->res >= esed->maxevents)
+ break;
/*
* Activate ep->ws before deactivating epi->ws to prevent
@@ -1658,42 +1659,42 @@ static __poll_t ep_send_events_proc(struct eventpoll *ep, struct list_head *head
list_del_init(&epi->rdllink);
- revents = ep_item_poll(epi, &pt, 1);
-
/*
* If the event mask intersect the caller-requested one,
* deliver the event to userspace. Again, ep_scan_ready_list()
- * is holding "mtx", so no operations coming from userspace
+ * is holding ep->mtx, so no operations coming from userspace
* can change the item.
*/
- if (revents) {
- if (__put_user(revents, &uevent->events) ||
- __put_user(epi->event.data, &uevent->data)) {
- list_add(&epi->rdllink, head);
- ep_pm_stay_awake(epi);
- if (!esed->res)
- esed->res = -EFAULT;
- return 0;
- }
- esed->res++;
- uevent++;
- if (epi->event.events & EPOLLONESHOT)
- epi->event.events &= EP_PRIVATE_BITS;
- else if (!(epi->event.events & EPOLLET)) {
- /*
- * If this file has been added with Level
- * Trigger mode, we need to insert back inside
- * the ready list, so that the next call to
- * epoll_wait() will check again the events
- * availability. At this point, no one can insert
- * into ep->rdllist besides us. The epoll_ctl()
- * callers are locked out by
- * ep_scan_ready_list() holding "mtx" and the
- * poll callback will queue them in ep->ovflist.
- */
- list_add_tail(&epi->rdllink, &ep->rdllist);
- ep_pm_stay_awake(epi);
- }
+ revents = ep_item_poll(epi, &pt, 1);
+ if (!revents)
+ continue;
+
+ if (__put_user(revents, &uevent->events) ||
+ __put_user(epi->event.data, &uevent->data)) {
+ list_add(&epi->rdllink, head);
+ ep_pm_stay_awake(epi);
+ if (!esed->res)
+ esed->res = -EFAULT;
+ return 0;
+ }
+ esed->res++;
+ uevent++;
+ if (epi->event.events & EPOLLONESHOT)
+ epi->event.events &= EP_PRIVATE_BITS;
+ else if (!(epi->event.events & EPOLLET)) {
+ /*
+ * If this file has been added with Level
+ * Trigger mode, we need to insert back inside
+ * the ready list, so that the next call to
+ * epoll_wait() will check again the events
+ * availability. At this point, no one can insert
+ * into ep->rdllist besides us. The epoll_ctl()
+ * callers are locked out by
+ * ep_scan_ready_list() holding "mtx" and the
+ * poll callback will queue them in ep->ovflist.
+ */
+ list_add_tail(&epi->rdllink, &ep->rdllist);
+ ep_pm_stay_awake(epi);
}
}
--
2.16.4
next prev parent reply other threads:[~2018-11-08 5:10 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-08 5:10 [PATCH -next 0/6] epoll: some miscellaneous optimizations Davidlohr Bueso
2018-11-08 5:10 ` [PATCH 1/6] fs/epoll: remove max_nests argument from ep_call_nested() Davidlohr Bueso
2018-11-08 5:10 ` Davidlohr Bueso [this message]
2018-11-08 5:10 ` [PATCH 3/6] fs/epoll: drop ovflist branch prediction Davidlohr Bueso
2018-11-08 5:10 ` [PATCH 4/6] fs/epoll: robustify ep->mtx held checks Davidlohr Bueso
2018-11-08 5:10 ` [PATCH 5/6] fs/epoll: reduce the scope of wq lock in epoll_wait() Davidlohr Bueso
2018-11-09 15:52 ` Davidlohr Bueso
2018-11-08 5:10 ` [PATCH 6/6] fs/epoll: avoid barrier after an epoll_wait(2) timeout Davidlohr Bueso
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