netdev - Re: [RFC net-next 1/4] net: Allow non parent devices to be used for ZC DMA

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Message-ID: <edff4079-294e-4428-a2fa-f69bf9578785@gmail.com>
Date: Tue, 8 Jul 2025 11:47:46 +0100
From: Pavel Begunkov <asml.silence@...il.com>
To: Mina Almasry <almasrymina@...gle.com>,
 Dragos Tatulea <dtatulea@...dia.com>
Cc: Parav Pandit <parav@...dia.com>, Jakub Kicinski <kuba@...nel.org>,
 Andrew Lunn <andrew+netdev@...n.ch>, "David S. Miller"
 <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 Paolo Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>,
 Saeed Mahameed <saeedm@...dia.com>, Tariq Toukan <tariqt@...dia.com>,
 Cosmin Ratiu <cratiu@...dia.com>,
 "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC net-next 1/4] net: Allow non parent devices to be used for
 ZC DMA

On 7/7/25 22:55, Mina Almasry wrote:
> On Mon, Jul 7, 2025 at 2:35 PM Dragos Tatulea <dtatulea@...dia.com> wrote:
...>> Right. My patches show that. But the issue raised by Parav is different:
>> different queues can belong to different DMA devices from different
>> PFs in the case of Multi PF netdev.
>>
>> io_uring can do it because it maps individual buffers to individual
>> queues. So it would be trivial to get the DMA device of each queue through
>> a new queue op.
>>
> 
> Right, devmem doesn't stop you from mapping individual buffers to
> individual queues. It just also supports mapping the same buffer to
> multiple queues. AFAIR, io_uring also supports mapping a single buffer
> to multiple queues, but I could easily be very wrong about that. It's

It doesn't, but it could benefit from sharing depending on userspace,
so it might eventually come to the same problem.

-- 
Pavel Begunkov