linux-kernel - Re: [PATCH v3 2/4] videobuf2-dma-streaming: new videobuf2 memory allocator

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Date:	Mon, 7 Jan 2013 18:15:00 -0200
From:	Mauro Carvalho Chehab <mchehab@...hat.com>
To:	Jonathan Corbet <corbet@....net>
Cc:	Alessandro Rubini <rubini@...dd.com>, federico.vaga@...il.com,
	m.szyprowski@...sung.com, mchehab@...radead.org, pawel@...iak.com,
	hans.verkuil@...co.com, giancarlo.asnaghi@...com,
	linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
	s.nawrocki@...sung.com
Subject: Re: [PATCH v3 2/4] videobuf2-dma-streaming: new videobuf2 memory
 allocator

Em Mon, 7 Jan 2013 12:40:50 -0700
Jonathan Corbet <corbet@....net> escreveu:

> On Mon, 7 Jan 2013 00:09:47 +0100
> Alessandro Rubini <rubini@...dd.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?

Regards,
Mauro
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