netdev - Re: [PATCH v6 02/15] net: generalise net

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Message-ID: <Zx9_iYLVnkyE05Hh@infradead.org>
Date: Mon, 28 Oct 2024 05:11:53 -0700
From: Christoph Hellwig <hch@...radead.org>
To: Pavel Begunkov <asml.silence@...il.com>
Cc: Christoph Hellwig <hch@...radead.org>, David Wei <dw@...idwei.uk>,
	io-uring@...r.kernel.org, netdev@...r.kernel.org,
	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>,
	Sumit Semwal <sumit.semwal@...aro.org>,
	Christian König <christian.koenig@....com>,
	linux-media@...r.kernel.org, dri-devel@...ts.freedesktop.org,
	linaro-mm-sig@...ts.linaro.org
Subject: Re: [PATCH v6 02/15] net: generalise net_iov chunk owners

On Thu, Oct 24, 2024 at 05:40:02PM +0100, Pavel Begunkov wrote:
> On 10/24/24 17:06, Christoph Hellwig wrote:
> > On Thu, Oct 24, 2024 at 03:23:06PM +0100, Pavel Begunkov wrote:
> > > > That's not what this series does.  It adds the new memory_provider_ops
> > > > set of hooks, with once implementation for dmabufs, and one for
> > > > io_uring zero copy.
> > > 
> > > First, it's not a _new_ abstraction over a buffer as you called it
> > > before, the abstraction (net_iov) is already merged.
> > 
> > Umm, it is a new ops vector.
> 
> I don't understand what you mean. Callback?

struct memory_provider_ops.  It's a method table or ops vetor, no
callbacks involved.

> Then please go ahead and take a look at the patchset in question
> and see how much of dmabuf handling is there comparing to pure
> networking changes. The point that it's a new set of API and lots
> of changes not related directly to dmabufs stand. dmabufs is useful
> there as an abstraction there, but it's a very long stretch saying
> that the series is all about it.

I did take a look, that's why I replied.

> > > on an existing network specific abstraction, which are not restricted to
> > > pages or anything specific in the long run, but the flow of which from
> > > net stack to user and back is controlled by io_uring. If you worry about
> > > abuse, io_uring can't even sanely initialise those buffers itself and
> > > therefore asking the page pool code to do that.
> > 
> > No, I worry about trying to io_uring for not good reason. This
> 
> It sounds that the argument is that you just don't want any
> io_uring APIs, I don't think you'd be able to help you with
> that.

No, that's complete misinterpreting what I'm saying.  Of course an
io_uring API is fine.  But tying low-level implementation details to
to is not.

> > pre-cludes in-kernel uses which would be extremly useful for
> 
> Uses of what? devmem TCP is merged, I'm not removing it,
> and the net_iov abstraction is in there, which can be potentially
> be reused by other in-kernel users if that'd even make sense.

How when you are hardcoding io uring memory registrations instead
of making them a generic dmabuf?  Which btw would also really help
with pre-registering the memry with the iommu to get good performance
in IOMMU-enabled setups.