netdev - Re: [PATCH net-next RFC v1 06/10] nvme-tcp: Add DDP data-path

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Date:   Sun, 8 Nov 2020 11:44:03 +0200
From:   Boris Pismenny <borispismenny@...il.com>
To:     Sagi Grimberg <sagi@...mberg.me>,
        Boris Pismenny <borisp@...lanox.com>, kuba@...nel.org,
        davem@...emloft.net, saeedm@...dia.com, hch@....de, axboe@...com,
        kbusch@...nel.org, viro@...iv.linux.org.uk, edumazet@...gle.com
Cc:     Yoray Zack <yorayz@...lanox.com>,
        Ben Ben-Ishay <benishay@...lanox.com>,
        boris.pismenny@...il.com, linux-nvme@...ts.infradead.org,
        netdev@...r.kernel.org, Or Gerlitz <ogerlitz@...lanox.com>
Subject: Re: [PATCH net-next RFC v1 06/10] nvme-tcp: Add DDP data-path



On 09/10/2020 1:29, Sagi Grimberg wrote:
>
>>   static int nvme_tcp_recv_data(struct nvme_tcp_queue *queue, struct sk_buff *skb,
>> @@ -1115,6 +1222,7 @@ static int nvme_tcp_try_send_cmd_pdu(struct nvme_tcp_request *req)
>>   	bool inline_data = nvme_tcp_has_inline_data(req);
>>   	u8 hdgst = nvme_tcp_hdgst_len(queue);
>>   	int len = sizeof(*pdu) + hdgst - req->offset;
>> +	struct request *rq = blk_mq_rq_from_pdu(req);
>>   	int flags = MSG_DONTWAIT;
>>   	int ret;
>>   
>> @@ -1123,6 +1231,10 @@ static int nvme_tcp_try_send_cmd_pdu(struct nvme_tcp_request *req)
>>   	else
>>   		flags |= MSG_EOR;
>>   
>> +	if (test_bit(NVME_TCP_Q_OFFLOADS, &queue->flags) &&
>> +	    blk_rq_nr_phys_segments(rq) && rq_data_dir(rq) == READ)
>> +		nvme_tcp_setup_ddp(queue, pdu->cmd.common.command_id, rq);
> I'd assume that this is something we want to setup in
> nvme_tcp_setup_cmd_pdu. Why do it here?
Our goal in placing it here is to keep both setup and teardown in the same thread.
This enables drivers to avoid locking for per-queue operations.