Re: [PATCH 1/3 v2] media: Add a cached version of the contiguous video buffers

["Richard Röjfors" <richard.rojfors@pelagicore.com>]

On 08/04/2010 12:34 PM, Pawel Osciak wrote:
>> Richard Röjfors<richard.rojfors@pelagicore.com>  wrote:
>> On 08/04/2010 11:50 AM, Pawel Osciak wrote:
>>>>
>>>> How do you propose to allocate the buffers? They need to be contiguous
>>>> and using uncached memory gave really bad performance.
>>>
>>> 829440 bytes is a quite a lot and one can't reliably depend on kmalloc
>>> to be able to allocate such big chunks of contiguous memory. Were you
>>> testing this on a freshly rebooted system?
>>
>> The systems have been running for a while, but not days.
>> I don't see why would dma_alloc_coherent work better than kmalloc?
>>
>
> In principle it wouldn't. It's just it's much less intensively used and
> allocates from a special area. Not really a bullet-proof solution either
> though, I agree.

So how do we move forward? I would like to see this kind of patch go in, it
obviously makes our video driver useful.

I could change and verify the patch using dma_alloc_noncoherent instead of
kmalloc. It would have the same "limitations" as todays' uncached  buffers.

--Richard