netdev - Re: [PATCH v4 net-next 07/21] nvme-tcp: Add DDP data-path

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Date:   Sun, 21 Feb 2021 13:44:11 +0200
From:   Boris Pismenny <borispismenny@...il.com>
To:     David Ahern <dsahern@...il.com>, Or Gerlitz <gerlitz.or@...il.com>
Cc:     Boris Pismenny <borisp@...lanox.com>,
        Jakub Kicinski <kuba@...nel.org>,
        David Miller <davem@...emloft.net>,
        Saeed Mahameed <saeedm@...dia.com>,
        Christoph Hellwig <hch@....de>,
        Sagi Grimberg <sagi@...mberg.me>, axboe@...com,
        Keith Busch <kbusch@...nel.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Eric Dumazet <edumazet@...gle.com>, smalin@...vell.com,
        boris.pismenny@...il.com, linux-nvme@...ts.infradead.org,
        Linux Netdev List <netdev@...r.kernel.org>,
        benishay@...dia.com, Or Gerlitz <ogerlitz@...dia.com>,
        yorayz@...dia.com, Ben Ben-Ishay <benishay@...lanox.com>,
        Or Gerlitz <ogerlitz@...lanox.com>,
        Yoray Zack <yorayz@...lanox.com>
Subject: Re: [PATCH v4 net-next 07/21] nvme-tcp: Add DDP data-path

On 17/02/2021 19:00, David Ahern wrote:
> On 2/17/21 7:01 AM, Or Gerlitz wrote:
>>>> @@ -1136,6 +1265,10 @@ static int nvme_tcp_try_send_cmd_pdu(struct nvme_tcp_request *req)
>>>>       else
>>>>               flags |= MSG_EOR;
>>>>
>>>> +     if (test_bit(NVME_TCP_Q_OFF_DDP, &queue->flags) &&
>>>> +         blk_rq_nr_phys_segments(rq) && rq_data_dir(rq) == READ)
>>>> +             nvme_tcp_setup_ddp(queue, pdu->cmd.common.command_id, rq);
>>>> +
>>>
>>> For consistency, shouldn't this be wrapped in the CONFIG_TCP_DDP check too?
>>
>> We tried to avoid the wrapping in some places where it was
>> possible to do without adding confusion, this one is a good
>> example IMOH.
>>
>>
> 
> The above (and other locations like it) can easily be put into a helper
> that has logic when the CONFIG is enabled and compiles out when not.
> Consistency makes for simpler, cleaner code for optional features.
> 

The above is consistent in the sense that we wrap only places that are
absolutely necessary, so as to avoid ifdefs as much as possible.

Specifically, here and in ddp_teardown, we will add a wrapper to reduce
clutter if offload is not used.