Re: [PATCH v2 2/5] mq-deadline: switch to use elevator lock

[Hannes Reinecke]

On 7/30/25 10:22, Yu Kuai wrote:
> From: Yu Kuai <yukuai3@xxxxxxxxxx>
>
> Replace the internal spinlock 'dd->lock' with the new spinlock in
> elevator_queue, there are no functional changes.
>
> Signed-off-by: Yu Kuai <yukuai3@xxxxxxxxxx>
> ---
>   block/mq-deadline.c | 58 +++++++++++++++++++++------------------------
>   1 file changed, 27 insertions(+), 31 deletions(-)
>
> diff --git a/block/mq-deadline.c b/block/mq-deadline.c
> index 9ab6c6256695..2054c023e855 100644
> --- a/block/mq-deadline.c
> +++ b/block/mq-deadline.c
> @@ -101,7 +101,7 @@ struct deadline_data {
>   	u32 async_depth;
>   	int prio_aging_expire;
>   
> -	spinlock_t lock;
> +	spinlock_t *lock;
>   };
>   
>   /* Maps an I/O priority class to a deadline scheduler priority. */
> @@ -213,7 +213,7 @@ static void dd_merged_requests(struct request_queue *q, struct request *req,
>   	const u8 ioprio_class = dd_rq_ioclass(next);
>   	const enum dd_prio prio = ioprio_class_to_prio[ioprio_class];
>   
> -	lockdep_assert_held(&dd->lock);
> +	lockdep_assert_held(dd->lock);
>   
>   	dd->per_prio[prio].stats.merged++;
>   
> @@ -253,7 +253,7 @@ static u32 dd_queued(struct deadline_data *dd, enum dd_prio prio)
>   {
>   	const struct io_stats_per_prio *stats = &dd->per_prio[prio].stats;
>   
> -	lockdep_assert_held(&dd->lock);
> +	lockdep_assert_held(dd->lock);
>   
>   	return stats->inserted - atomic_read(&stats->completed);
>   }
> @@ -323,7 +323,7 @@ static struct request *__dd_dispatch_request(struct deadline_data *dd,
>   	enum dd_prio prio;
>   	u8 ioprio_class;
>   
> -	lockdep_assert_held(&dd->lock);
> +	lockdep_assert_held(dd->lock);
>   
>   	if (!list_empty(&per_prio->dispatch)) {
>   		rq = list_first_entry(&per_prio->dispatch, struct request,
> @@ -434,7 +434,7 @@ static struct request *dd_dispatch_prio_aged_requests(struct deadline_data *dd,
>   	enum dd_prio prio;
>   	int prio_cnt;
>   
> -	lockdep_assert_held(&dd->lock);
> +	lockdep_assert_held(dd->lock);
>   
>   	prio_cnt = !!dd_queued(dd, DD_RT_PRIO) + !!dd_queued(dd, DD_BE_PRIO) +
>   		   !!dd_queued(dd, DD_IDLE_PRIO);
> @@ -466,10 +466,9 @@ static struct request *dd_dispatch_request(struct blk_mq_hw_ctx *hctx)
>   	struct request *rq;
>   	enum dd_prio prio;
>   
> -	spin_lock(&dd->lock);
>   	rq = dd_dispatch_prio_aged_requests(dd, now);
>   	if (rq)
> -		goto unlock;
> +		return rq;
>   
>   	/*
>   	 * Next, dispatch requests in priority order. Ignore lower priority
> @@ -481,9 +480,6 @@ static struct request *dd_dispatch_request(struct blk_mq_hw_ctx *hctx)
>   			break;
>   	}
>   
> -unlock:
> -	spin_unlock(&dd->lock);
> -
>   	return rq;
>   }
>   
> @@ -538,9 +534,9 @@ static void dd_exit_sched(struct elevator_queue *e)
>   		WARN_ON_ONCE(!list_empty(&per_prio->fifo_list[DD_READ]));
>   		WARN_ON_ONCE(!list_empty(&per_prio->fifo_list[DD_WRITE]));
>   
> -		spin_lock(&dd->lock);
> +		spin_lock(dd->lock);
>   		queued = dd_queued(dd, prio);
> -		spin_unlock(&dd->lock);
> +		spin_unlock(dd->lock);
>   
>   		WARN_ONCE(queued != 0,
>   			  "statistics for priority %d: i %u m %u d %u c %u\n",

Do you still need 'dd->lock'? Can't you just refer to the lock from the
elevator_queue structure directly?

Cheers,

Hannes
--
Dr. Hannes Reinecke                  Kernel Storage Architect
hare@xxxxxxx                                +49 911 74053 688
SUSE Software Solutions GmbH, Frankenstr. 146, 90461 Nürnberg
HRB 36809 (AG Nürnberg), GF: I. Totev, A. McDonald, W. Knoblich