[PATCH 7/8] md/raid5: raise MAX_STRIPE_BATCH from 8 to 32

[Hiroshi Nishida <nishidafmly@gmail.com>]

handle_active_stripes() dequeues up to MAX_STRIPE_BATCH stripes under
device_lock per pass, then processes them after dropping the lock.
Raising the batch from 8 to 32 amortizes each device_lock acquisition
over more stripes, reducing lock cycles per unit of stripe work.

The worker-spawn heuristic in raid5_wakeup_stripe_thread() also divided
by MAX_STRIPE_BATCH; split it into a separate STRIPE_BATCH_WORKERS=8 so
the spawn sensitivity is preserved unchanged while the batch size grows.

Assisted-by: Claude:claude-opus-4-8 [Claude Code]
Signed-off-by: Hiroshi Nishida <nishidafmly@gmail.com>
---
 drivers/md/raid5.c | 2 +-
 drivers/md/raid5.h | 3 ++-
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index c8787ab7b309..ad6230415af3 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -210,7 +210,7 @@ static void raid5_wakeup_stripe_thread(struct stripe_head *sh)
 	/* at least one worker should run to avoid race */
 	queue_work_on(sh->cpu, raid5_wq, &group->workers[0].work);
 
-	thread_cnt = group->stripes_cnt / MAX_STRIPE_BATCH - 1;
+	thread_cnt = group->stripes_cnt / STRIPE_BATCH_WORKERS - 1;
 	/* wakeup more workers */
 	for (i = 1; i < conf->worker_cnt_per_group && thread_cnt > 0; i++) {
 		if (group->workers[i].working == false) {
diff --git a/drivers/md/raid5.h b/drivers/md/raid5.h
index 7aeba1fc7f09..1f37dabd727b 100644
--- a/drivers/md/raid5.h
+++ b/drivers/md/raid5.h
@@ -496,7 +496,8 @@ struct disk_info {
 #define BYPASS_THRESHOLD	1
 #define NR_HASH			(PAGE_SIZE / sizeof(struct hlist_head))
 #define HASH_MASK		(NR_HASH - 1)
-#define MAX_STRIPE_BATCH	8
+#define MAX_STRIPE_BATCH	32	/* stripes per handle_active_stripes pass */
+#define STRIPE_BATCH_WORKERS	8	/* stripes-per-worker threshold for spawning */
 #define RAID5_SYNC_WINDOW	32	/* stripes to pre-submit per sync_request call */
 
 /* NR_STRIPE_HASH_LOCKS must be a power of two, since
-- 
2.43.0