netdev - Re: [PATCH net-next v8 00/17] io

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Message-ID: <41da1af6-edf0-4c8c-ad72-4f51f1056da3@gmail.com>
Date: Wed, 4 Dec 2024 18:59:31 +0000
From: Pavel Begunkov <asml.silence@...il.com>
To: David Wei <dw@...idwei.uk>, io-uring@...r.kernel.org,
 netdev@...r.kernel.org
Cc: Jens Axboe <axboe@...nel.dk>, Jakub Kicinski <kuba@...nel.org>,
 Paolo Abeni <pabeni@...hat.com>, "David S. Miller" <davem@...emloft.net>,
 Eric Dumazet <edumazet@...gle.com>, Jesper Dangaard Brouer
 <hawk@...nel.org>, David Ahern <dsahern@...nel.org>,
 Mina Almasry <almasrymina@...gle.com>,
 Stanislav Fomichev <stfomichev@...il.com>, Joe Damato <jdamato@...tly.com>,
 Pedro Tammela <pctammela@...atatu.com>
Subject: Re: [PATCH net-next v8 00/17] io_uring zero copy rx

On 12/4/24 17:21, David Wei wrote:
> This patchset adds support for zero copy rx into userspace pages using
> io_uring, eliminating a kernel to user copy.
> We configure a page pool that a driver uses to fill a hw rx queue to
> hand out user pages instead of kernel pages. Any data that ends up
> hitting this hw rx queue will thus be dma'd into userspace memory
> directly, without needing to be bounced through kernel memory. 'Reading'
> data out of a socket instead becomes a _notification_ mechanism, where
> the kernel tells userspace where the data is. The overall approach is
> similar to the devmem TCP proposal.
> 
> This relies on hw header/data split, flow steering and RSS to ensure
> packet headers remain in kernel memory and only desired flows hit a hw
> rx queue configured for zero copy. Configuring this is outside of the
> scope of this patchset.
> 
> We share netdev core infra with devmem TCP. The main difference is that
> io_uring is used for the uAPI and the lifetime of all objects are bound
> to an io_uring instance. Data is 'read' using a new io_uring request
> type. When done, data is returned via a new shared refill queue. A zero
> copy page pool refills a hw rx queue from this refill queue directly. Of
> course, the lifetime of these data buffers are managed by io_uring
> rather than the networking stack, with different refcounting rules.
> 
> This patchset is the first step adding basic zero copy support. We will
> extend this iteratively with new features e.g. dynamically allocated
> zero copy areas, THP support, dmabuf support, improved copy fallback,
> general optimisations and more.
> 
> In terms of netdev support, we're first targeting Broadcom bnxt. Patches
> aren't included since Taehee Yoo has already sent a more comprehensive
> patchset adding support in [1]. Google gve should already support this,
> and Mellanox mlx5 support is WIP pending driver changes.

It misses some changes and has unaddressed concerns from Jakub,
so that should rather be an RFC.

-- 
Pavel Begunkov