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SubjectRe: [PATCH] WIP! media: uvcvideo: Use dma_alloc_noncontiguos API
HI Christoph

On Tue, Nov 24, 2020 at 12:35 PM Christoph Hellwig <> wrote:
> On Wed, Nov 18, 2020 at 03:25:46PM +0100, Ricardo Ribalda wrote:
> > On architectures where the is no coherent caching such as ARM use the
> > dma_alloc_noncontiguos API and handle manually the cache flushing using
> > dma_sync_single().
> >
> > With this patch on the affected architectures we can measure up to 20x
> > performance improvement in uvc_video_copy_data_work().
> This has a bunch of crazy long lines, but otherwise looks fine to me.

That is easy to solve :)

> >
> > Signed-off-by: Ricardo Ribalda <>
> > ---
> >
> > This patch depends on dma_alloc_contiguous API1315351diffmboxseries
> How do we want to proceed? Do the media maintainers want to pick up
> that patch? Should I pick up the media patch in the dma-mapping tree?

I was hoping that you could answer that question :).

Do you have other use-cases than linux-media in mind?

I think Sergey wants to experiment also with vb2, to figure out how
much it affects it.
His change will be much more complicated than mine thought, there are
more cornercases there.

> Can you respost a combined series to get started?

Sure. Shall I also include the profiling patch?

Best regards
Ricardo Ribalda

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