lkml.org 
[lkml]   [2018]   [Nov]   [16]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH 1/1] Improve kernfs_notify() poll notification latency
Date
kernfs_notify() does two notifications: poll and fsnotify. Originally,
both notifications were done from scheduled work context and all that
kernfs_notify() did was schedule the work.

This patch simply moves the poll notification from the scheduled work
handler to kernfs_notify(). The fsnotify notification still needs to be
done from scheduled work context because it can sleep (it needs to lock
a mutex).

If the poll notification is time critical (the notified thread needs to
wake as quickly as possible), it's better to do it from kernfs_notify()
directly. One example is calling sysfs_notify_dirent() from a hardware
interrupt handler to wake up a thread and handle the interrupt in user
space.

Signed-off-by: Radu Rendec <radu.rendec@gmail.com>
---
fs/kernfs/file.c | 23 +++++++++++------------
1 file changed, 11 insertions(+), 12 deletions(-)

diff --git a/fs/kernfs/file.c b/fs/kernfs/file.c
index dbf5bc250bfd..f8d5021a652e 100644
--- a/fs/kernfs/file.c
+++ b/fs/kernfs/file.c
@@ -857,7 +857,6 @@ static __poll_t kernfs_fop_poll(struct file *filp, poll_table *wait)
static void kernfs_notify_workfn(struct work_struct *work)
{
struct kernfs_node *kn;
- struct kernfs_open_node *on;
struct kernfs_super_info *info;
repeat:
/* pop one off the notify_list */
@@ -871,17 +870,6 @@ static void kernfs_notify_workfn(struct work_struct *work)
kn->attr.notify_next = NULL;
spin_unlock_irq(&kernfs_notify_lock);

- /* kick poll */
- spin_lock_irq(&kernfs_open_node_lock);
-
- on = kn->attr.open;
- if (on) {
- atomic_inc(&on->event);
- wake_up_interruptible(&on->poll);
- }
-
- spin_unlock_irq(&kernfs_open_node_lock);
-
/* kick fsnotify */
mutex_lock(&kernfs_mutex);

@@ -934,10 +922,21 @@ void kernfs_notify(struct kernfs_node *kn)
{
static DECLARE_WORK(kernfs_notify_work, kernfs_notify_workfn);
unsigned long flags;
+ struct kernfs_open_node *on;

if (WARN_ON(kernfs_type(kn) != KERNFS_FILE))
return;

+ /* kick poll immediately */
+ spin_lock_irqsave(&kernfs_open_node_lock, flags);
+ on = kn->attr.open;
+ if (on) {
+ atomic_inc(&on->event);
+ wake_up_interruptible(&on->poll);
+ }
+ spin_unlock_irqrestore(&kernfs_open_node_lock, flags);
+
+ /* schedule work to kick fsnotify */
spin_lock_irqsave(&kernfs_notify_lock, flags);
if (!kn->attr.notify_next) {
kernfs_get(kn);
--
2.17.2
\
 
 \ /
  Last update: 2018-11-16 03:12    [W:0.055 / U:0.800 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site