Re: [PATCH 3/4] blk-mq: use hw tag for scheduling if hw tag space is big enough

[Omar Sandoval]

On Fri, Apr 28, 2017 at 11:15:38PM +0800, Ming Lei wrote:
> When tag space of one device is big enough, we use hw tag
> directly for I/O scheduling.
> 
> Now the decision is made if hw queue depth is not less than
> q->nr_requests and the tag set isn't shared.
> 
> Signed-off-by: Ming Lei <ming....@redhat.com>
> ---
>  block/blk-mq-sched.c |  8 ++++++++
>  block/blk-mq-sched.h | 15 +++++++++++++++
>  block/blk-mq.c       | 18 +++++++++++++++++-
>  3 files changed, 40 insertions(+), 1 deletion(-)
> 
> diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c
> index 45a675f07b8b..4681e27c127e 100644
> --- a/block/blk-mq-sched.c
> +++ b/block/blk-mq-sched.c
> @@ -507,6 +507,7 @@ int blk_mq_init_sched(struct request_queue *q, struct 
> elevator_type *e)
>       struct elevator_queue *eq;
>       unsigned int i;
>       int ret;
> +     bool auto_hw_tag;
>  
>       if (!e) {
>               q->elevator = NULL;
> @@ -519,7 +520,14 @@ int blk_mq_init_sched(struct request_queue *q, struct 
> elevator_type *e)
>        */
>       q->nr_requests = 2 * BLKDEV_MAX_RQ;
>  
> +     auto_hw_tag = blk_mq_sched_may_use_hw_tag(q);
> +
>       queue_for_each_hw_ctx(q, hctx, i) {
> +             if (auto_hw_tag)
> +                     hctx->flags |= BLK_MQ_F_SCHED_USE_HW_TAG;
> +             else
> +                     hctx->flags &= ~BLK_MQ_F_SCHED_USE_HW_TAG;
> +
>               ret = blk_mq_sched_alloc_tags(q, hctx, i);
>               if (ret)
>                       goto err;

I think you should also clear the BLK_MQ_F_SCHED_USE_HW_TAG flag in
blk_mq_exit_sched()?