[dm-devel] [PATCH] dm: dm_table_unplug_all optimization

[Mike Anderson <andmike linux vnet ibm com>]

Performance optimization for high contention of the q->queue_lock under
certain workloads.

Signed-off-by: Mike Anderson <andmike linux vnet ibm com>
---

 drivers/md/dm-table.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
index e75b143..f4c8c1b 100644
--- a/drivers/md/dm-table.c
+++ b/drivers/md/dm-table.c
@@ -1012,7 +1012,8 @@ void dm_table_unplug_all(struct dm_table *t)
 	list_for_each_entry(dd, devices, list) {
 		struct request_queue *q = bdev_get_queue(dd->bdev);
 
-		blk_unplug(q);
+		if (blk_queue_plugged(q))
+			blk_unplug(q);
 	}
 }