[Mesa-dev] Mesa (master): 29 new commits

[Alex Deucher]

On Thu, Apr 14, 2016 at 3:29 AM, Michel Dänzer <michel at daenzer.net> wrote:
> On 14.04.2016 11:37, Michel Dänzer wrote:
>> On 12.04.2016 21:33, Marek =?UNKNOWN?B?T2zFocOhaw==?= wrote:
>>>
>>> URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=5a4b74d1ba2c156766a7a5dbfef099c7db5d6694
>>> Author: Marek Olšák <marek.olsak at amd.com>
>>> Date:   Mon Apr 11 19:56:07 2016 +0200
>>>
>>>     gallium/radeon: relax requirements on VRAM placements on APUs
>>
>> This change caused a bunch of ARB_shader_load_image_store piglit tests
>> to fail on my Kaveri, see some examples below. The incorrect values
>> seem consistent.
>>
>> I suppose some buffers end up in GTT instead of VRAM with this
>> change, but I'm not sure how that could cause problems. Any ideas?
>
> Also, with the code modified to use GTT only for everything but
> (potential) scanout buffers, the performance of Unigine Valley and the
> Unreal Engine 4 Elemental demo is reduced by about 30%. So the premise
> that GTT is about as fast as VRAM doesn't seem to hold true in practice
> (at least with Kaveri and presumably other (pre-)CIK APUs; maybe it's
> better with Carrizo and newer), which means that this change may cause
> performance of long-running processes to drop significantly over time.

We need to make sure the buffers end up in WC GTT.  The cache snoops
for coherent GTT reduce performance.

Alex

>
> Given all these issues, I'm afraid it may be better to revert this
> change for now, until we have a better plan for dealing with this.
>
>
> --
> Earthling Michel Dänzer               |               http://www.amd.com
> Libre software enthusiast             |             Mesa and X developer
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