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

[Marek Olšák]

On Thu, Apr 14, 2016 at 3:21 PM, Alex Deucher <alexdeucher at gmail.com> wrote:
> 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.

The numbers are with GTT WC.

Marek