md: Replace md_thread's wait queue with the swait variant

Commit Message

Jinpu Wang March 5, 2024, 8:24 a.m. UTC

From: Florian-Ewald Mueller <[e-mail]>

Replace md_thread's wait_event()/wake_up() related calls with their
simple swait~ variants to improve performance as well as memory and
stack footprint.

Use the IDLE state for the worker thread put to sleep instead of
misusing the INTERRUPTIBLE state combined with flushing signals
just for not contributing to system's cpu load-average stats.

Also check for sleeping thread before attempting its wake_up in
md_wakeup_thread() for avoiding unnecessary spinlock contention.

With this patch (backported) on a kernel 6.1, the IOPS improved
by around 4% with raid1 and/or raid5, in high IO load scenarios.

Signed-off-by: Florian-Ewald Mueller <[e-mail]>
Signed-off-by: Jack Wang <[e-mail]>
---
 drivers/md/md.c | 23 +++++++----------------
 drivers/md/md.h |  2 +-
 2 files changed, 8 insertions(+), 17 deletions(-)

Patch

diff --git a/drivers/md/md.c b/drivers/md/md.c
index 48ae2b1cb57a..edc28767a9d7 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -7970,22 +7970,12 @@  static int md_thread(void *arg)
 	 * many dirty RAID5 blocks.
 	 */
 
-	allow_signal(SIGKILL);
 	while (!kthread_should_stop()) {
 
-		/* We need to wait INTERRUPTIBLE so that
-		 * we don't add to the load-average.
-		 * That means we need to be sure no signals are
-		 * pending
-		 */
-		if (signal_pending(current))
-			flush_signals(current);
-
-		wait_event_interruptible_timeout
-			(thread->wqueue,
-			 test_bit(THREAD_WAKEUP, &thread->flags)
-			 || kthread_should_stop() || kthread_should_park(),
-			 thread->timeout);
+		swait_event_idle_timeout_exclusive(thread->wqueue,
+			test_bit(THREAD_WAKEUP, &thread->flags) ||
+			kthread_should_stop() || kthread_should_park(),
+			thread->timeout);
 
 		clear_bit(THREAD_WAKEUP, &thread->flags);
 		if (kthread_should_park())
@@ -8017,7 +8007,8 @@  void md_wakeup_thread(struct md_thread __rcu *thread)
 	if (t) {
 		pr_debug("md: waking up MD thread %s.\n", t->tsk->comm);
 		set_bit(THREAD_WAKEUP, &t->flags);
-		wake_up(&t->wqueue);
+		if (swq_has_sleeper(&thread->wqueue))
+			swake_up_one(&thread->wqueue);
 	}
 	rcu_read_unlock();
 }
@@ -8032,7 +8023,7 @@  struct md_thread *md_register_thread(void (*run) (struct md_thread *),
 	if (!thread)
 		return NULL;
 
-	init_waitqueue_head(&thread->wqueue);
+	init_swait_queue_head(&thread->wqueue);
 
 	thread->run = run;
 	thread->mddev = mddev;
diff --git a/drivers/md/md.h b/drivers/md/md.h
index b2076a165c10..1dc01bc5c038 100644
--- a/drivers/md/md.h
+++ b/drivers/md/md.h
@@ -716,7 +716,7 @@  static inline void sysfs_unlink_rdev(struct mddev *mddev, struct md_rdev *rdev)
 struct md_thread {
 	void			(*run) (struct md_thread *thread);
 	struct mddev		*mddev;
-	wait_queue_head_t	wqueue;
+	struct swait_queue_head	wqueue;
 	unsigned long		flags;
 	struct task_struct	*tsk;
 	unsigned long		timeout;