On 4/8/23 08:58, Bart Van Assche wrote:
> Let the I/O scheduler control which requests are dispatched.
Well, that is the main function of the IO scheduler already. So could you
develop the commit message here to explain in more details which case this is
changing ?
>
> Cc: Christoph Hellwig <hch@xxxxxx>
> Cc: Damien Le Moal <damien.lemoal@xxxxxxxxxxxxxxxxxx>
> Cc: Ming Lei <ming.lei@xxxxxxxxxx>
> Cc: Mike Snitzer <snitzer@xxxxxxxxxx>
> Signed-off-by: Bart Van Assche <bvanassche@xxxxxxx>
> ---
> block/blk-mq.c | 21 +++++++++------------
> include/linux/blk-mq.h | 5 +++--
> 2 files changed, 12 insertions(+), 14 deletions(-)
>
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index 250556546bbf..57315395434b 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -1426,15 +1426,7 @@ static void blk_mq_requeue_work(struct work_struct *work)
>
> rq->rq_flags &= ~RQF_SOFTBARRIER;
> list_del_init(&rq->queuelist);
> - /*
> - * If RQF_DONTPREP, rq has contained some driver specific
> - * data, so insert it to hctx dispatch list to avoid any
> - * merge.
> - */
> - if (rq->rq_flags & RQF_DONTPREP)
> - blk_mq_request_bypass_insert(rq, false, false);
> - else
> - blk_mq_sched_insert_request(rq, true, false, false);
> + blk_mq_sched_insert_request(rq, /*at_head=*/true, false, false);
> }
>
> while (!list_empty(&rq_list)) {
> @@ -2065,9 +2057,14 @@ bool blk_mq_dispatch_rq_list(struct blk_mq_hw_ctx *hctx, struct list_head *list,
> if (nr_budgets)
> blk_mq_release_budgets(q, list);
>
> - spin_lock(&hctx->lock);
> - list_splice_tail_init(list, &hctx->dispatch);
> - spin_unlock(&hctx->lock);
> + if (!q->elevator) {
> + spin_lock(&hctx->lock);
> + list_splice_tail_init(list, &hctx->dispatch);
> + spin_unlock(&hctx->lock);
> + } else {
> + q->elevator->type->ops.insert_requests(hctx, list,
> + /*at_head=*/true);
Dispatch at head = true ? Why ? This seems wrong. It may be valid for the
requeue case (even then, I am not convinced), but looks very wrong for the
regular dispatch case.
> + }
>
> /*
> * Order adding requests to hctx->dispatch and checking
> diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
> index 5e6c79ad83d2..3a3bee9085e3 100644
> --- a/include/linux/blk-mq.h
> +++ b/include/linux/blk-mq.h
> @@ -64,8 +64,9 @@ typedef __u32 __bitwise req_flags_t;
> #define RQF_RESV ((__force req_flags_t)(1 << 23))
>
> /* flags that prevent us from merging requests: */
> -#define RQF_NOMERGE_FLAGS \
> - (RQF_STARTED | RQF_SOFTBARRIER | RQF_FLUSH_SEQ | RQF_SPECIAL_PAYLOAD)
> +#define RQF_NOMERGE_FLAGS \
> + (RQF_STARTED | RQF_SOFTBARRIER | RQF_FLUSH_SEQ | RQF_DONTPREP | \
> + RQF_SPECIAL_PAYLOAD)
>
> enum mq_rq_state {
> MQ_RQ_IDLE = 0,
