Re: commit 7ffb791423c7 breaks steam game

[Balbir Singh]

On 3/17/25 00:09, Bert Karwatzki wrote:
> This is related to the admgpu.gttsize. My laptop has the maximum amount 
> of memory (64G) and usually gttsize is half of main memory size. I just 
> tested with cmdline="nokaslr amdgpi.gttsize=2048" and the problem does 
> not occur. So I did some more testing with varying gttsize and got this
> for the built-in GPU
> 
> 08:00.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI]
> Cezanne [Radeon Vega Series / Radeon Vega Mobile Series] (rev c5)
> 
> (nokaslr is always enabeld)
> gttssize   input behaviour
>  2048		GOOD
>  2064		GOOD
>  2080		SEMIBAD (i.e. noticeable input lag but not as bad as below)
>  3072		BAD
>  4096		BAD
>  8192		BAD
> 16384		BAD
> 
> As the build-in GPU has ~512 VRAM there seems to be problems when gttsize >
> 4*VRAM so I tested for the discrete GPU with 8G of VRAM
> gttsize   input behaviour
> 49152		GOOD
> 64000		GOOD
> 
> So for the discrete GPU increasing gttsize does no reproduce the bug.
> 

Very interesting, I am not a GTT expert, but with these experiments do you
find anything interesting in

/sys/kernel/debug/x86/pat_memtype_list?

It's weird that you don't see any issues in Xorg (Xfce), just the games.
May be we should get help from the amd-gfx experts to further diagnose/debug
the interaction of nokaslr with the game.

Balbir