[Mesa-dev] [PATCH 4/6] gallium/radeon: fix performance of buffer readbacks

[Michel Dänzer]

On 10/02/17 08:27 PM, Marek Olšák wrote:
> On Fri, Feb 10, 2017 at 12:22 PM, Emil Velikov <emil.l.velikov at gmail.com> wrote:
>>  On 9 February 2017 at 11:56, Marek Olšák <maraeo at gmail.com> wrote:
>>> From: Marek Olšák <marek.olsak at amd.com>
>>>
>>> We want cached GTT for all non-persistent read mappings.
>>> Set level = 0 on purpose.
>>>
>>> Use dma_copy, because resource_copy_region causes a failure in the PBO
>>> read of piglit/getteximage-luminance.
>>>
>>> If Rocket League used the READ flag, it should get cached GTT.
>>>
>> Does this patch resolve/mitigate the reported performance issues with
>> Rocket League ?
>>
>> Strictly speaking performance patches are a no-go for stable, although
>> we had exceptions in the past.
>> I will pick this up, but for future do provide numbers which indicate
>> the severity of the issue.
> 
> It will help only if Rocket League is fixed to use GL_MAP_READ_BIT. It
> doesn't fix the current release of Rocket League.

That's incorrect, it always used GL_MAP_READ_BIT. So this fix should
(and reportedly does) help with unpatched Rocket League.

As can be seen from https://bugs.freedesktop.org/show_bug.cgi?id=97879
(which should have been referenced by the commit log :), the problem is
freezes of up to several seconds, which makes the game essentially
unplayable, especially for online multiplayer.

OTOH the game itself has now been fixed to no longer run into the
problem, and I suspect most users will probably get the game update
before any future Mesa stable release.


-- 
Earthling Michel Dänzer               |               http://www.amd.com
Libre software enthusiast             |             Mesa and X developer