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

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Message-ID: <20130106230947.GA17979@mail.gnudd.com>
Date:	Mon, 7 Jan 2013 00:09:47 +0100
From:	Alessandro Rubini <rubini@...dd.com>
To:	federico.vaga@...il.com
Cc:	mchehab@...hat.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, corbet@....net,
	s.nawrocki@...sung.com
Subject: Re: [PATCH v3 2/4] videobuf2-dma-streaming: new videobuf2 memory
 allocator

> The problem is that on the sta2x11 architecture only the first 
> 512MB are available through the PCI bus, but the allocator can allocate memory 
> for DMA above this limit. By using GFP_DMA flags the allocation take place 
> under the 16MB so it works.

Still, you are not running the upstream allocator.  IIUC, you added a
"gfp_t" field in the platform data or somewhere, so the sta2x11 can
request GFP_DMA to be OR'd, while other users remain unaffected.  Will
you please submit the patch to achieve that?

> I cannot do performance test at the moment because I don't have the time, so I 
> cannot personally justify the presence of a new allocator.

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.

> I will propose V4 patches soon.

thanks
/alessandro
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