Merge branch 'md-6.12-raid5-opt' into md-6.12

From Artur:

The wait_for_overlap wait queue is currently used in two cases, which
are not really related:
 - waiting for actual overlapping bios, which uses R5_Overlap bit,
 - waiting for events related to reshape.

Handling every write request in raid5_make_request() involves adding to
and removing from this wait queue, which uses a spinlock. With fast
storage and multiple submitting threads the contention on this lock is
noticeable.

This patch series aims to resolve this by separating the two cases
mentioned above and using this wait queue only when reshape is in
progress.

The results when testing 4k random writes on raid5 with null_blk
(8 jobs, qd=64, group_thread_cnt=8):
before: 463k IOPS
after:  523k IOPS

The improvement is not huge with this series alone but it is just one of
the bottlenecks. When applied onto some other changes I'm working on, it
allowed to go from 845k IOPS to 975k IOPS on the same test.

* md-6.12-raid5-opt:
  md/raid5: rename wait_for_overlap to wait_for_reshape
  md/raid5: only add to wq if reshape is in progress
  md/raid5: use wait_on_bit() for R5_Overlap
Signed-off-by: Song Liu <song@kernel.org>

drivers/md/raid5-cache.c

@@ -2798,7 +2798,6 @@ void r5c_finish_stripe_write_out(struct r5conf *conf,
 {
 	struct r5l_log *log = READ_ONCE(conf->log);
 	int i;
-	int do_wakeup = 0;
 	sector_t tree_index;
 	void __rcu **pslot;
 	uintptr_t refcount;
@@ -2815,7 +2814,7 @@ void r5c_finish_stripe_write_out(struct r5conf *conf,
 	for (i = sh->disks; i--; ) {
 		clear_bit(R5_InJournal, &sh->dev[i].flags);
 		if (test_and_clear_bit(R5_Overlap, &sh->dev[i].flags))
-			do_wakeup = 1;
+			wake_up_bit(&sh->dev[i].flags, R5_Overlap);
 	}
 
 	/*
@@ -2828,9 +2827,6 @@ void r5c_finish_stripe_write_out(struct r5conf *conf,
 		if (atomic_dec_and_test(&conf->pending_full_writes))
 			md_wakeup_thread(conf->mddev->thread);
 
-	if (do_wakeup)
-		wake_up(&conf->wait_for_overlap);
-
 	spin_lock_irq(&log->stripe_in_journal_lock);
 	list_del_init(&sh->r5c);
 	spin_unlock_irq(&log->stripe_in_journal_lock);

drivers/md/raid5.h

@@ -668,7 +668,7 @@ struct r5conf {
 	struct llist_head	released_stripes;
 	wait_queue_head_t	wait_for_quiescent;
 	wait_queue_head_t	wait_for_stripe;
-	wait_queue_head_t	wait_for_overlap;
+	wait_queue_head_t	wait_for_reshape;
 	unsigned long		cache_state;
 	struct shrinker		*shrinker;
 	int			pool_size; /* number of disks in stripeheads in pool */