linux-kernel - Re: [PATCH 04/10] gpu: nova-core: Add a slice-buffer (sbuffer) datastructure

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Message-ID: <kxriy5tmcdpbop674gt55tmcfsvdy52dnw6dw6svemj4a52dtf@xhvjfrcjxbgw>
Date: Mon, 8 Sep 2025 21:31:23 +1000
From: Alistair Popple <apopple@...dia.com>
To: Alice Ryhl <aliceryhl@...gle.com>
Cc: dri-devel@...ts.freedesktop.org, dakr@...nel.org, acourbot@...dia.com, 
	Miguel Ojeda <ojeda@...nel.org>, Alex Gaynor <alex.gaynor@...il.com>, 
	Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>, 
	Björn Roy Baron <bjorn3_gh@...tonmail.com>, Benno Lossin <lossin@...nel.org>, 
	Andreas Hindborg <a.hindborg@...nel.org>, Trevor Gross <tmgross@...ch.edu>, 
	David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>, 
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, Maxime Ripard <mripard@...nel.org>, 
	Thomas Zimmermann <tzimmermann@...e.de>, John Hubbard <jhubbard@...dia.com>, 
	Joel Fernandes <joelagnelf@...dia.com>, Timur Tabi <ttabi@...dia.com>, linux-kernel@...r.kernel.org, 
	nouveau@...ts.freedesktop.org
Subject: Re: [PATCH 04/10] gpu: nova-core: Add a slice-buffer (sbuffer)
 datastructure

On 2025-09-07 at 20:54 +1000, Alice Ryhl <aliceryhl@...gle.com> wrote...
> On Wed, Aug 27, 2025 at 06:20:01PM +1000, Alistair Popple wrote:
> > From: Joel Fernandes <joelagnelf@...dia.com>
> > 
> > A data structure that can be used to write across multiple slices which
> > may be out of order in memory. This lets SBuffer user correctly and
> > safely write out of memory order, without error-prone tracking of
> > pointers/offsets.
> > 
> >  let mut buf1 = [0u8; 3];
> >  let mut buf2 = [0u8; 5];
> >  let mut sbuffer = SBuffer::new([&mut buf1[..], &mut buf2[..]]);
> > 
> >  let data = b"hellowo";
> >  let result = sbuffer.write(data);
> > 
> > An internal conversion of gsp.rs to use this resulted in a nice -ve delta:
> > gsp.rs: 37 insertions(+), 99 deletions(-)
> > 
> > Co-developed-by: Alistair Popple <apopple@...dia.com>
> > Signed-off-by: Alistair Popple <apopple@...dia.com>
> > Signed-off-by: Joel Fernandes <joelagnelf@...dia.com>
> 
> This seems like duplication of the logic in rust/kernel/iov_iter.rs [1].

Conceptually I guess there is some overlap. The thing that's different here
is we don't have any C version of the iovec struct or iov_iter, and AFAICT [1]
doesn't provide any way of creating one from within Rust code.

> Alice
> 
> [1]: https://lore.kernel.org/r/20250822-iov-iter-v5-0-6ce4819c2977@google.com