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

From: Aurelien Aptel <[email-masked]>
Date: Mon, 29 Apr 2024 14:35:33 +0300

Sagi Grimberg <[email-masked]> writes:
> This is not simply a steering rule that can be overwritten at any point?

No, unlike steering rules, the offload resources cannot be moved to a
different queue.

In order to move it we will need to re-create the queue and the
resources assigned to it.  We will consider to improve the HW/FW/SW to
allow this in future versions.

> 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?

You're correct, it doesn't need to exist *if* we use sk->incoming_cpu,
which at the time it is used, is the wrong value.
The right value for cfg->io_cpu is nvme_queue->io_cpu.

So either:
- we do that and thus keep cfg->io_cpu.
- or we remove cfg->io_cpu, and we offload the socket from
  nvme_tcp_io_work() where the io_cpu is implicitly going to be
  the current CPU.

Thanks