Re: [PATCH 4/5] nvme: quiesce namespace queue in parallel

Sagi Grimberg
2021-11-22T08:07:28Z

On 11/19/21 4:18 AM, Ming Lei wrote:
> Chao Leng reported that in case of lots of namespaces, it may take quite a
> while for nvme_stop_queues() to quiesce all namespace queues.
>
> Improve nvme_stop_queues() by running quiesce in parallel, and just wait
> once if global quiesce wait is allowed.
>
> Link: https://lore.kernel.org/linux-block/cc732195-c053-9ce4-e1a7-e7f6dcf762ac@huawei.com/
> Reported-by: Chao Leng <lengchao@huawei.com>
> Signed-off-by: Ming Lei <ming.lei@redhat.com>
> ---
> drivers/nvme/host/core.c | 9 ++++++---
> 1 file changed, 6 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
> index 4b5de8f5435a..06741d3ed72b 100644
> --- a/drivers/nvme/host/core.c
> +++ b/drivers/nvme/host/core.c
> @@ -4517,9 +4517,7 @@ static void nvme_start_ns_queue(struct nvme_ns *ns)
> static void nvme_stop_ns_queue(struct nvme_ns *ns)
> {
> if (!test_and_set_bit(NVME_NS_STOPPED, &ns->flags))
> - blk_mq_quiesce_queue(ns->queue);
> - else
> - blk_mq_wait_quiesce_done(ns->queue);
> + blk_mq_quiesce_queue_nowait(ns->queue);
> }
>
> /*
> @@ -4620,6 +4618,11 @@ void nvme_stop_queues(struct nvme_ctrl *ctrl)
> down_read(&ctrl->namespaces_rwsem);
> list_for_each_entry(ns, &ctrl->namespaces, list)
> nvme_stop_ns_queue(ns);
> + list_for_each_entry(ns, &ctrl->namespaces, list) {
> + blk_mq_wait_quiesce_done(ns->queue);
> + if (blk_mq_global_quiesce_wait(ns->queue))
> + break;
> + }
> up_read(&ctrl->namespaces_rwsem);

Can you quantify how much of a difference it is to do rcu_read_unlock()
for every queue? The big improvement here is that it is done in parallel
instead of serially. Just wandering if it is worth the less than elegant
interface...