Re: [PATCH 7/7] blk-mq: use plug for devices that implement ->commits_rqs()

[Ming Lei <ming.lei@redhat.com>]

On Wed, Nov 28, 2018 at 06:35:38AM -0700, Jens Axboe wrote:
> If we have that hook, we know the driver handles bd->last == true in
> a smart fashion. If it does, even for multiple hardware queues, it's
> a good idea to flush batches of requests to the device, if we have
> batches of requests from the submitter.
> 
> Signed-off-by: Jens Axboe <axboe@kernel.dk>
> ---
>  block/blk-mq.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index 9e1045152e45..091557a43d53 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -1945,7 +1945,12 @@ static blk_qc_t blk_mq_make_request(struct request_queue *q, struct bio *bio)
>  		/* bypass scheduler for flush rq */
>  		blk_insert_flush(rq);
>  		blk_mq_run_hw_queue(data.hctx, true);
> -	} else if (plug && q->nr_hw_queues == 1) {
> +	} else if (plug && (q->nr_hw_queues == 1 || q->mq_ops->commit_rqs)) {
> +		/*
> +		 * Use plugging if we have a ->commit_rqs() hook as well,
> +		 * as we know the driver uses bd->last in a smart
> +		 * fashion.
> +		 */
>  		unsigned int request_count = plug->rq_count;
>  		struct request *last = NULL;
>  
> -- 
> 2.17.1
> 

Reviewed-by: Ming Lei <ming.lei@redhat.com>

thanks,
Ming