Re: [PATCH 1/4] block: add mq_ops->queue_rqs hook

[Jens Axboe <axboe@kernel.dk>]

On 11/17/21 1:20 AM, Ming Lei wrote:
> On Tue, Nov 16, 2021 at 08:38:04PM -0700, Jens Axboe wrote:
>> If we have a list of requests in our plug list, send it to the driver in
>> one go, if possible. The driver must set mq_ops->queue_rqs() to support
>> this, if not the usual one-by-one path is used.
>>
>> Signed-off-by: Jens Axboe <axboe@kernel.dk>
>> ---
>>  block/blk-mq.c         | 17 +++++++++++++++++
>>  include/linux/blk-mq.h |  8 ++++++++
>>  2 files changed, 25 insertions(+)
>>
>> diff --git a/block/blk-mq.c b/block/blk-mq.c
>> index 9b4e79e2ac1e..005715206b16 100644
>> --- a/block/blk-mq.c
>> +++ b/block/blk-mq.c
>> @@ -2208,6 +2208,19 @@ static void blk_mq_plug_issue_direct(struct blk_plug *plug, bool from_schedule)
>>  	int queued = 0;
>>  	int errors = 0;
>>  
>> +	/*
>> +	 * Peek first request and see if we have a ->queue_rqs() hook. If we
>> +	 * do, we can dispatch the whole plug list in one go. We already know
>> +	 * at this point that all requests belong to the same queue, caller
>> +	 * must ensure that's the case.
>> +	 */
>> +	rq = rq_list_peek(&plug->mq_list);
>> +	if (rq->q->mq_ops->queue_rqs) {
>> +		rq->q->mq_ops->queue_rqs(&plug->mq_list);
>> +		if (rq_list_empty(plug->mq_list))
>> +			return;
>> +	}
>> +
> 
> Then BLK_MQ_F_TAG_QUEUE_SHARED isn't handled as before for multiple NVMe
> NS.

Can you expand? If we have multiple namespaces in the plug list, we have
multiple queues. There's no direct issue of the list if that's the case.
Or maybe I'm missing what you mean here?

-- 
Jens Axboe