netdev - Re: [RFC PATCH v2 01/11] net: add netdev netlink api to bind dma-buf to a net device

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Date: Thu, 10 Aug 2023 19:19:38 -0700
From: Mina Almasry <almasrymina@...gle.com>
To: "Samudrala, Sridhar" <sridhar.samudrala@...el.com>
Cc: netdev@...r.kernel.org, linux-media@...r.kernel.org, 
	dri-devel@...ts.freedesktop.org, "David S. Miller" <davem@...emloft.net>, 
	Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
	Jesper Dangaard Brouer <hawk@...nel.org>, Ilias Apalodimas <ilias.apalodimas@...aro.org>, 
	Arnd Bergmann <arnd@...db.de>, David Ahern <dsahern@...nel.org>, 
	Willem de Bruijn <willemdebruijn.kernel@...il.com>, Sumit Semwal <sumit.semwal@...aro.org>, 
	Christian König <christian.koenig@....com>, 
	Jason Gunthorpe <jgg@...pe.ca>, Hari Ramakrishnan <rharix@...gle.com>, 
	Dan Williams <dan.j.williams@...el.com>, Andy Lutomirski <luto@...nel.org>, stephen@...workplumber.org, 
	sdf@...gle.com, Amritha Nambiar <amritha.nambiar@...el.com>
Subject: Re: [RFC PATCH v2 01/11] net: add netdev netlink api to bind dma-buf
 to a net device

On Thu, Aug 10, 2023 at 9:09 AM Samudrala, Sridhar
<sridhar.samudrala@...el.com> wrote:
>
>
>
> On 8/9/2023 6:57 PM, Mina Almasry wrote:
> > API takes the dma-buf fd as input, and binds it to the netdevice. The
> > user can specify the rx queue to bind the dma-buf to. The user should be
> > able to bind the same dma-buf to multiple queues, but that is left as
> > a (minor) TODO in this iteration.
>
> To support binding dma-buf fd to multiple queues, can we extend/change
> this interface to bind dma-buf fd to a napi_id? Amritha is currently
> working on a patchset that exposes napi_id's and their association with
> the queues.
>
> https://lore.kernel.org/netdev/169059098829.3736.381753570945338022.stgit@anambiarhost.jf.intel.com/
>

Thank you Sridhar,

I think honestly implementing multiple rx queue binding is trivial,
even without the napi_id association. The user should be able to call
the bind-rx API multiple times with the same dma-buf to bind to
multiple queues, or I can convert the queue-idx to a multi-attr
netlink attribute to let the user specify multiple rx queues in 1
call.

Without doing some homework it's not immediately obvious to me that
coupling the dma-buf binding with the napi_id is necessary or
advantageous. Is there a reason coupling those is better?

It seems like napi_id can also refer to TX queues, and binding a
dma-buf with a TX queue doesn't make much sense to me. For TX we need
to couple the dma-buf with the netdev that's sending the dma-buf data,
but not a specific TX queue on the netdev, I think.

-- 
Thanks,
Mina