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

[Marek Olšák]

On Tue, Feb 14, 2017 at 3:05 PM, Emil Velikov <emil.l.velikov at gmail.com> wrote:
> On 13 February 2017 at 03:24, Michel Dänzer <michel at daenzer.net> wrote:
>> 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.
>>
> I'm concerned about the reports that although this(?) commit makes the
> stalls shorter, it also decreases performance (do to ~80%).
>
> Fabio (Oibaf) is fairly responsive so getting the extra patch in his
> PPA should be trivial. I'd imagine that others, say padoka (Paulo),
> would also gladly assist.

The lower performance might be due to the game using GL_MAP_READ_BIT
even when the flag isn't necessary.

Marek