[PATCH 1/1] nvme-multipath: Skip nr_active increments in RETRY disposition

[Amit Chaudhary]

For queue-depth I/O policy, this patch fixes unbalanced I/Os across
nvme multipaths.

Issue Description:

The RETRY disposition incorrectly increments ns->ctrl->nr_active
counter and reinitializes iostat start-time. In such cases nr_active
counter never goes back to zero until that path disconnects and
reconnects.

Such a path is not chosen for new I/Os if multiple RETRY cases on a given
a path cause its queue-depth counter to be artificially higher compared
to other paths. This leads to unbalanced I/Os across paths.

The patch skips calling nvme_mpath_start_request() on a RETRY disposition
if nvme_req(rq)->retries counter is non-zero. This avoids reincrementing
nr_active and also from restarting io_stat start time.

base-commit: e989a3da2d371a4b6597ee8dee5c72e407b4db7a
Fixes: d4d957b53d91eeb ("nvme-multipath: support io stats on the mpath device")
Signed-off-by: Amit Chaudhary <achaudhary at purestorage.com>
Reviewed-by: Randy Jennings <randyj at purestorage.com>
---
 drivers/nvme/host/nvme.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/nvme/host/nvme.h b/drivers/nvme/host/nvme.h
index 102fae6a231c..6ca6529ba83a 100644
--- a/drivers/nvme/host/nvme.h
+++ b/drivers/nvme/host/nvme.h
@@ -1150,7 +1150,7 @@ static inline void nvme_hwmon_exit(struct nvme_ctrl *ctrl)
 
 static inline void nvme_start_request(struct request *rq)
 {
-	if (rq->cmd_flags & REQ_NVME_MPATH)
+	if ((rq->cmd_flags & REQ_NVME_MPATH) && (!nvme_req(rq)->retries))
 		nvme_mpath_start_request(rq);
 	blk_mq_start_request(rq);
 }
-- 
2.43.0