On Mon, Nov 26, 2018 at 09:35:51AM -0700, Jens Axboe wrote:
> blk-mq passes information to the hardware about any given request being
> the last that we will issue in this sequence. The point is that hardware
> can defer costly doorbell type writes to the last request. But if we run
> into errors issuing a sequence of requests, we may never send the request
> with bd->last == true set. For that case, we need a hook that tells the
> hardware that nothing else is coming right now.
>
> For failures returned by the drivers ->queue_rq() hook, the driver is
> responsible for flushing pending requests, if it uses bd->last to
> optimize that part. This works like before, no changes there.
Reviewed-by: Omar Sandoval <osan...@fb.com>
> Signed-off-by: Jens Axboe <ax...@kernel.dk>
> ---
> include/linux/blk-mq.h | 10 ++++++++++
> 1 file changed, 10 insertions(+)
>
> diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
> index ca0520ca6437..1fd139b65a6e 100644
> --- a/include/linux/blk-mq.h
> +++ b/include/linux/blk-mq.h
> @@ -117,6 +117,7 @@ struct blk_mq_queue_data {
>
> typedef blk_status_t (queue_rq_fn)(struct blk_mq_hw_ctx *,
> const struct blk_mq_queue_data *);
> +typedef void (commit_rqs_fn)(struct blk_mq_hw_ctx *);
> /* takes rq->cmd_flags as input, returns a hardware type index */
> typedef int (rq_flags_to_type_fn)(struct request_queue *, unsigned int);
> typedef bool (get_budget_fn)(struct blk_mq_hw_ctx *);
> @@ -144,6 +145,15 @@ struct blk_mq_ops {
> */
> queue_rq_fn *queue_rq;
>
> + /*
> + * If a driver uses bd->last to judge when to submit requests to
> + * hardware, it must define this function. In case of errors that
> + * make us stop issuing further requests, this hook serves the
> + * purpose of kicking the hardware (which the last request otherwise
> + * would have done).
> + */
> + commit_rqs_fn *commit_rqs;
> +
> /*
> * Return a queue map type for the given request/bio flags
> */
> --
> 2.17.1
>
