[PATCH rfc 3/4] nvme-core: reduce io failover time

[Sagi Grimberg]

From: Chao Leng <lengchao at huawei.com>

We test nvme over roce fail over with multipath when 1000 namespaces
configured, io pause more than 10 seconds. The reason: nvme_stop_queues
will quiesce all queues for each namespace when io timeout cause path
error. Quiesce queue wait all ongoing dispatches finished through
synchronize_rcu, need more than 10 milliseconds for each wait,
thus io pause more than 10 seconds.

To reduce io pause time, nvme_stop_queues use
blk_mq_quiesce_queue_nowait to quiesce the queue, nvme_stop_queues wait
all ongoing dispatches completed after all queues has been quiesced.

Signed-off-by: Chao Leng <lengchao at huawei.com>
Signed-off-by: Sagi Grimberg <sagi at grimberg.me>
---
 drivers/nvme/host/core.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
index f1a76bad226e..0796c448a3c3 100644
--- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c
@@ -4548,8 +4548,13 @@ void nvme_stop_queues(struct nvme_ctrl *ctrl)
 
 	down_read(&ctrl->namespaces_rwsem);
 	list_for_each_entry(ns, &ctrl->namespaces, list)
-		blk_mq_quiesce_queue(ns->queue);
+		blk_mq_quiesce_queue_nowait(ns->queue);
 	up_read(&ctrl->namespaces_rwsem);
+	/*
+	 * BLK_MQ_F_BLOCKING drivers should never call us
+	 */
+	WARN_ON_ONCE(ctrl->tagset.flags & BLK_MQ_F_BLOCKING);
+	synchronize_rcu();
 }
 EXPORT_SYMBOL_GPL(nvme_stop_queues);
 
-- 
2.25.1