Messages in this thread |  | | Date | Tue, 08 Jan 2013 07:50:41 +0100 | From | Marek Szyprowski <> | Subject | Re: [PATCH v3 2/4] videobuf2-dma-streaming: new videobuf2 memory allocator |
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On 1/7/2013 9:15 PM, Mauro Carvalho Chehab wrote: > Em Mon, 7 Jan 2013 12:40:50 -0700 > Jonathan Corbet <corbet@lwn.net> escreveu: > > > On Mon, 7 Jan 2013 00:09:47 +0100 > > Alessandro Rubini <rubini@gnudd.com> wrote: > > > > > I don't expect you'll see serious performance differences on the PC. I > > > think ARM users will have better benefits, due to the different cache > > > architecture. You told me Jon measured meaningful figures on a Marvel > > > CPU. > > > > It made the difference between 10 frames per second with the CPU running > > flat out and 30fps mostly idle. I think that probably counts as > > meaningful, yeah...:) > > Couldn't this performance difference be due to the usage of GFP_DMA inside > the VB2 code, like Federico's new patch series is proposing? > > If not, why are there a so large performance penalty?
Nope, this was caused rather by a very poor CPU access to non-cached (aka 'coherent') memory and the way the video data has been accessed/read with CPU.
Best regards -- Marek Szyprowski Samsung Poland R&D Center
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