Re: [PATCH 4/4] nvme: add support for mq_ops->queue_rqs()

[Max Gurtovoy <mgurtovoy@nvidia.com>]

On 12/16/2021 11:08 AM, Christoph Hellwig wrote:
> On Wed, Dec 15, 2021 at 09:24:21AM -0700, Jens Axboe wrote:
>> +	spin_lock(&nvmeq->sq_lock);
>> +	while (!rq_list_empty(*rqlist)) {
>> +		struct request *req = rq_list_pop(rqlist);
>> +		struct nvme_iod *iod = blk_mq_rq_to_pdu(req);
>> +
>> +		memcpy(nvmeq->sq_cmds + (nvmeq->sq_tail << nvmeq->sqes),
>> +				absolute_pointer(&iod->cmd), sizeof(iod->cmd));
>> +		if (++nvmeq->sq_tail == nvmeq->q_depth)
>> +			nvmeq->sq_tail = 0;
> So this doesn't even use the new helper added in patch 2?  I think this
> should call nvme_sq_copy_cmd().

I also noticed that.

So need to decide if to open code it or use the helper function.

Inline helper sounds reasonable if you have 3 places that will use it.

> The rest looks identical to the incremental patch I posted, so I guess
> the performance degration measured on the first try was a measurement
> error?

giving 1 dbr for a batch of N commands sounds good idea. Also for RDMA host.

But how do you moderate it ? what is the batch_sz <--> time_to_wait 
algorithm ?