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

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Message-ID: <226d1cd7-bd35-4773-8f1c-d03f9c870133@kernel.org>
Date: Thu, 31 Jul 2025 15:22:44 +0900
From: Damien Le Moal <dlemoal@...nel.org>
To: Hannes Reinecke <hare@...e.de>, Yu Kuai <yukuai1@...weicloud.com>,
 jack@...e.cz, tj@...nel.org, josef@...icpanda.com, axboe@...nel.dk,
 yukuai3@...wei.com
Cc: cgroups@...r.kernel.org, linux-block@...r.kernel.org,
 linux-kernel@...r.kernel.org, yi.zhang@...wei.com, yangerkun@...wei.com,
 johnny.chenyi@...wei.com
Subject: Re: [PATCH v2 2/5] mq-deadline: switch to use elevator lock

On 7/31/25 3:20 PM, Hannes Reinecke wrote:
> On 7/30/25 10:22, Yu Kuai wrote:
>> From: Yu Kuai <yukuai3@...wei.com>
>>
>> Replace the internal spinlock 'dd->lock' with the new spinlock in
>> elevator_queue, there are no functional changes.
>>
>> Signed-off-by: Yu Kuai <yukuai3@...wei.com>
>> ---
>>   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?

Indeed. Little inline helpers for locking/unlocking q->elevator->lock would be
nice.

-- 
Damien Le Moal
Western Digital Research