[Devel] [RFC PATCH vz9 4/5] ploop: reduce the time lock is hold, taking it only to protect data

[Alexander Atanasov]

Currently lock is taken once for all pios submitted(code block),
move it to protect only the list insertion (data).
The goal is to reduce lock contention on the deferred lock as
it is in the top of lock stats.

Signed-off-by: Alexander Atanasov <alexander.atanasov at virtuozzo.com>
---
 drivers/md/dm-ploop-map.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/md/dm-ploop-map.c b/drivers/md/dm-ploop-map.c
index e8e543d566d1..b0f60a6a6fd7 100644
--- a/drivers/md/dm-ploop-map.c
+++ b/drivers/md/dm-ploop-map.c
@@ -340,8 +340,9 @@ static void ploop_dispatch_pio(struct ploop *ploop, struct pio *pio,
 			       bool *is_data, bool *is_flush)
 {
 	struct list_head *list = &ploop->pios[pio->queue_list_id];
+	unsigned long flags;
 
-	lockdep_assert_held(&ploop->deferred_lock);
+	lockdep_assert_not_held(&ploop->deferred_lock);
 	WARN_ON_ONCE(pio->queue_list_id >= PLOOP_LIST_COUNT);
 
 	if (pio->queue_list_id == PLOOP_LIST_FLUSH)
@@ -349,23 +350,22 @@ static void ploop_dispatch_pio(struct ploop *ploop, struct pio *pio,
 	else
 		*is_data = true;
 
+	spin_lock_irqsave(&ploop->deferred_lock, flags);
 	list_add_tail(&pio->list, list);
+	spin_unlock_irqrestore(&ploop->deferred_lock, flags);
 }
 
 void ploop_dispatch_pios(struct ploop *ploop, struct pio *pio,
 			 struct list_head *pio_list)
 {
 	bool is_data = false, is_flush = false;
-	unsigned long flags;
 
-	spin_lock_irqsave(&ploop->deferred_lock, flags);
 	if (pio)
 		ploop_dispatch_pio(ploop, pio, &is_data, &is_flush);
 	if (pio_list) {
 		while ((pio = ploop_pio_list_pop(pio_list)) != NULL)
 			ploop_dispatch_pio(ploop, pio, &is_data, &is_flush);
 	}
-	spin_unlock_irqrestore(&ploop->deferred_lock, flags);
 
 	if (is_data)
 		queue_work(ploop->wq, &ploop->worker);
-- 
2.43.0