On Fri, Jan 05, 2018 at 02:56:38PM -0700, Jens Axboe wrote:
> Don't pass in the hardware queue to __dd_dispatch_request(), since it
> leads the reader to believe that we are returning a request for that
> specific hardware queue. That's not how mq-deadline works, the state
> for determining which request to serve next is shared across all
> hardware queues for a device.
Reviewed-by: Omar Sandoval <osandov@xxxxxx>
> Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
>
> ---
>
> diff --git a/block/mq-deadline.c b/block/mq-deadline.c
> index d56972e8ebda..c56f211c8440 100644
> --- a/block/mq-deadline.c
> +++ b/block/mq-deadline.c
> @@ -267,9 +267,8 @@ deadline_next_request(struct deadline_data *dd, int data_dir)
> * deadline_dispatch_requests selects the best request according to
> * read/write expire, fifo_batch, etc
> */
> -static struct request *__dd_dispatch_request(struct blk_mq_hw_ctx *hctx)
> +static struct request *__dd_dispatch_request(struct deadline_data *dd)
> {
> - struct deadline_data *dd = hctx->queue->elevator->elevator_data;
> struct request *rq, *next_rq;
> bool reads, writes;
> int data_dir;
> @@ -372,13 +371,19 @@ static struct request *__dd_dispatch_request(struct blk_mq_hw_ctx *hctx)
> return rq;
> }
>
> +/*
> + * One confusing aspect here is that we get called for a specific
> + * hardware queue, but we return a request that may not be for a
> + * different hardware queue. This is because mq-deadline has shared
> + * state for all hardware queues, in terms of sorting, FIFOs, etc.
> + */
> static struct request *dd_dispatch_request(struct blk_mq_hw_ctx *hctx)
> {
> struct deadline_data *dd = hctx->queue->elevator->elevator_data;
> struct request *rq;
>
> spin_lock(&dd->lock);
> - rq = __dd_dispatch_request(hctx);
> + rq = __dd_dispatch_request(dd);
> spin_unlock(&dd->lock);
>
> return rq;
>
> --
> Jens Axboe
>
