Re: [PATCH v3 2/4] videobuf2-dma-streaming: new videobuf2 memoryallocator

[Jonathan Corbet]

On Tue, 08 Jan 2013 07:50:41 +0100
Marek Szyprowski <m.szyprowski@xxxxxxxxxxx> wrote:

> > 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.

Exactly.  Uncached memory *hurts*, especially if you're having to touch it
all with the CPU.

jon
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