Re: [PATCH] drm/ttm: Only try to preserve caching in moves in the same space

[Thomas Hellstrom <thellstrom@vmware.com>]

Jerome Glisse wrote:
> On Mon, Feb 01, 2010 at 11:35:21AM +1000, Dave Airlie wrote:
>   
>> On Thu, Jan 28, 2010 at 7:26 PM, Luca Barbieri <luca@luca-barbieri.com> wrote:
>>     
>>> Currently TTM tries to preserve the previous caching even for moves
>>> between unrelated memory spaces.
>>>
>>> This results for instance in moves from VRAM to PCIE GART changing
>>> system memory to WC state needlessly.
>>>
>>> This patch changes TTM to only try to preserve caching if moving from
>>> system/TT to system/TT.
>>>
>>> In theory, we should also do that if moving between two device memory
>>> spaces that are backend by the same physical memory area.
>>> However, I'm not sure how to do that in the current TTM framework and
>>> I suspect no card/driver uses memory spaces in that way.
>>>       
>> Thomas or Jerome (since I think placement changes were you), any
>> chance of ack or review?
>>
>> Dave.
>>
>>     
>
> I think i will NACK, the idea to avoid switching to WC is good but i think it
> can be achieve with current code by using cleverly the infrastructure.
>   
I agree with Jerome. It *should* be possible to have the driver control 
this sort of thing depending on what triggered the validate / move call.

Thanks,
Thomas


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