netdev - Re: [PATCH v12 07/26] nvme-tcp: Add DDP offload control path

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Message-ID: <2ae6c96b-2b05-583e-55bd-2d20133b9b37@grimberg.me>
Date: Wed, 9 Aug 2023 10:39:42 +0300
From: Sagi Grimberg <sagi@...mberg.me>
To: Chaitanya Kulkarni <chaitanyak@...dia.com>,
 Aurelien Aptel <aaptel@...dia.com>, Shai Malin <smalin@...dia.com>
Cc: "davem@...emloft.net" <davem@...emloft.net>,
 Boris Pismenny <borisp@...dia.com>,
 "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
 "kuba@...nel.org" <kuba@...nel.org>,
 "aurelien.aptel@...il.com" <aurelien.aptel@...il.com>,
 "hch@....de" <hch@....de>, "axboe@...com" <axboe@...com>,
 "malin1024@...il.com" <malin1024@...il.com>, Or Gerlitz
 <ogerlitz@...dia.com>, Yoray Zack <yorayz@...dia.com>,
 "linux-nvme@...ts.infradead.org" <linux-nvme@...ts.infradead.org>,
 Gal Shalom <galshalom@...dia.com>, Max Gurtovoy <mgurtovoy@...dia.com>,
 "kbusch@...nel.org" <kbusch@...nel.org>
Subject: Re: [PATCH v12 07/26] nvme-tcp: Add DDP offload control path



On 8/1/23 05:25, Chaitanya Kulkarni wrote:
> On 7/12/23 09:14, Aurelien Aptel wrote:
>> From: Boris Pismenny <borisp@...dia.com>
>>
>> This commit introduces direct data placement offload to NVME
>> TCP. There is a context per queue, which is established after the
>> handshake using the sk_add/del NDOs.
>>
>> Additionally, a resynchronization routine is used to assist
>> hardware recovery from TCP OOO, and continue the offload.
>> Resynchronization operates as follows:
>>
>> 1. TCP OOO causes the NIC HW to stop the offload
>>
>> 2. NIC HW identifies a PDU header at some TCP sequence number,
>> and asks NVMe-TCP to confirm it.
>> This request is delivered from the NIC driver to NVMe-TCP by first
>> finding the socket for the packet that triggered the request, and
>> then finding the nvme_tcp_queue that is used by this routine.
>> Finally, the request is recorded in the nvme_tcp_queue.
>>
>> 3. When NVMe-TCP observes the requested TCP sequence, it will compare
>> it with the PDU header TCP sequence, and report the result to the
>> NIC driver (resync), which will update the HW, and resume offload
>> when all is successful.
>>
>> Some HW implementation such as ConnectX-7 assume linear CCID (0...N-1
>> for queue of size N) where the linux nvme driver uses part of the 16
>> bit CCID for generation counter. To address that, we use the existing
>> quirk in the nvme layer when the HW driver advertises if the device is
>> not supports the full 16 bit CCID range.
>>
>> Furthermore, we let the offloading driver advertise what is the max hw
>> sectors/segments via ulp_ddp_limits.
>>
>> A follow-up patch introduces the data-path changes required for this
>> offload.
>>
>> Socket operations need a netdev reference. This reference is
>> dropped on NETDEV_GOING_DOWN events to allow the device to go down in
>> a follow-up patch.
>>
>> Signed-off-by: Boris Pismenny <borisp@...dia.com>
>> Signed-off-by: Ben Ben-Ishay <benishay@...dia.com>
>> Signed-off-by: Or Gerlitz <ogerlitz@...dia.com>
>> Signed-off-by: Yoray Zack <yorayz@...dia.com>
>> Signed-off-by: Shai Malin <smalin@...dia.com>
>> Signed-off-by: Aurelien Aptel <aaptel@...dia.com>
>> Reviewed-by: Chaitanya Kulkarni <kch@...dia.com>
>> ---
> 
> For NVMe related code :-
> 
> Offload feature is configurable and maybe not be turned on in the absence
> of the H/W. In order to keep the nvme/host/tcp.c file small to only handle
> core related functionality, I wonder if we should to move tcp-offload code
> into it's own file say nvme/host/tcp-offload.c ?

Maybe. it wouldn't be tcp_offload.c but rather tcp_ddp.c because its not
offloading the tcp stack but rather doing direct data placement.

If we are going to do that it will pollute nvme.h or add a common
header file, which is something I'd like to avoid if possible.