netdev - Re: [PATCH v24 01/20] net: Introduce direct data placement tcp offload

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Date: Sun, 28 Apr 2024 11:15:38 +0300
From: Sagi Grimberg <sagi@...mberg.me>
To: Aurelien Aptel <aaptel@...dia.com>, linux-nvme@...ts.infradead.org,
 netdev@...r.kernel.org, hch@....de, kbusch@...nel.org, axboe@...com,
 chaitanyak@...dia.com, davem@...emloft.net, kuba@...nel.org
Cc: Boris Pismenny <borisp@...dia.com>, aurelien.aptel@...il.com,
 smalin@...dia.com, malin1024@...il.com, ogerlitz@...dia.com,
 yorayz@...dia.com, galshalom@...dia.com, mgurtovoy@...dia.com,
 edumazet@...gle.com, pabeni@...hat.com, dsahern@...nel.org, ast@...nel.org,
 jacob.e.keller@...el.com
Subject: Re: [PATCH v24 01/20] net: Introduce direct data placement tcp
 offload



On 26/04/2024 10:21, Aurelien Aptel wrote:
> Hi Sagi,
>
> Sagi Grimberg <sagi@...mberg.me> writes:
>>> +     config->io_cpu = sk->sk_incoming_cpu;
>>> +     ret = netdev->netdev_ops->ulp_ddp_ops->sk_add(netdev, sk, config);
>> Still don't understand why you need the io_cpu config if you are passing
>> the sk to the driver...
> With our HW we cannot move the offload queues to a different CPU without
> destroying and recreating the offload resources on the new CPU.

This is not simply a steering rule that can be overwritten at any point?

>
> Since the connection is created from a different CPU then the io queue
> thread, we cannot predict which CPU we should create our offload context
> on.
>
> Ideally, io_cpu should be set to nvme_queue->io_cpu or it should be removed
> and the socket should be offloaded from the io thread. What do you
> prefer?

I was simply referring to the fact that you set config->io_cpu from 
sk->sk_incoming_cpu
and then you pass sk (and config) to .sk_add, so why does this 
assignment need to
exist here and not below the interface down at the driver?