[PATCH RFC] nvme-multipath: optimize path selection in queue-depth policy

Move the zero-depth check inside the optimized path case to enable early
exit. It avoids redundant condition checks for non-optimized paths, and
eliminates the per-iteration check at the end of the loop, improving the
performance.

Cc: Aviv Coro <[email protected]>
Cc: Bart Van Assche <[email protected]>
Cc: Benjamin Marzinski <[email protected]>
Cc: Brian Bunker <[email protected]>
Cc: Caleb Sander <[email protected]>
Cc: Chaitanya Kulkarni <[email protected]>
Cc: Chris Leech <[email protected]>
Cc: Christophe Varoqui <[email protected]>
Cc: Christoph Hellwig <[email protected]>
Cc: Clayton Skaggs <[email protected]>
Cc: Constantine Gavrilov <[email protected]>
Cc: Daniel Wagner <[email protected]>
Cc: David Santamaría Rogado <[email protected]>
Cc: Dmitry V. Levin <[email protected]>
Cc: Ewan D. Milne <[email protected]>
Cc: Ewan Milne <[email protected]>
Cc: Hannes Reinecke <[email protected]>
Cc: James Smart <[email protected]>
Cc: Jens Axboe <[email protected]>
Cc: John Meneghini <[email protected]>
Cc: Jyoti Rani <[email protected]>
Cc: Keith Busch <[email protected]>
Cc: Li Xiaokeng <[email protected]>
Cc: Marco Patalano <[email protected]>
Cc: Martin Belanger <[email protected]>
Cc: Martin George <[email protected]>
Cc: Martin Wilck <[email protected]>
Cc: Matthias Rudolph <[email protected]>
Cc: Maurizio Lombardi <[email protected]>
Cc: NetApp RDAC team <[email protected]>
Cc: Nilay Shroff <[email protected]>
Cc: Randy Jennings <[email protected]>
Cc: Sagi Grimberg <[email protected]>
Cc: Simon Schricker <[email protected]>
Cc: Steven Schremmer <[email protected]>
Cc: Thomas Song <[email protected]>
Cc: Uday Shankar <[email protected]>
Cc: Vasuki Manikarnike <[email protected]>
Cc: Wayne Berthiaume <[email protected]>
Cc: Zou Ming <[email protected]>
Cc: BLOCK-ML <[email protected]>
Cc: DM_DEVEL-ML <[email protected]>
Cc: NVME-ML <[email protected]>
Cc: SCSI-ML <[email protected]>
Signed-off-by: Xose Vazquez Perez <[email protected]>
---
Status: Compile-tested only. UNTESTED on real hardware.

[I do not have access to this kind of hardware]

Feedback and testing are highly welcome.
---
 drivers/nvme/host/multipath.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/drivers/nvme/host/multipath.c b/drivers/nvme/host/multipath.c
index 263161cb8ac0..7d212f6e865d 100644
--- a/drivers/nvme/host/multipath.c
+++ b/drivers/nvme/host/multipath.c
@@ -409,6 +409,8 @@ static struct nvme_ns *nvme_queue_depth_path(struct nvme_ns_head *head)
 				min_depth_opt = depth;
 				best_opt = ns;
 			}
+			if (min_depth_opt == 0)
+				goto out;
 			break;
 		case NVME_ANA_NONOPTIMIZED:
 			if (depth < min_depth_nonopt) {
@@ -419,11 +421,8 @@ static struct nvme_ns *nvme_queue_depth_path(struct nvme_ns_head *head)
 		default:
 			break;
 		}
-
-		if (min_depth_opt == 0)
-			return best_opt;
 	}
-
+out:
 	return best_opt ? best_opt : best_nonopt;
 }
 
-- 
2.54.0