linux-kernel - Re: commit 7ffb791423c7 breaks steam game

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Message-ID: <9be36dfab79b17e108f71d51a6ebf39073e110c6.camel@web.de>
Date: Sun, 16 Mar 2025 14:09:26 +0100
From: Bert Karwatzki <spasswolf@....de>
To: Alex Deucher <alexdeucher@...il.com>, Balbir Singh <balbirs@...dia.com>
Cc: Ingo Molnar <mingo@...nel.org>, Kees Cook <kees@...nel.org>, Bjorn
 Helgaas	 <bhelgaas@...gle.com>, Linus Torvalds
 <torvalds@...ux-foundation.org>, Peter Zijlstra <peterz@...radead.org>,
 Andy Lutomirski <luto@...nel.org>, linux-kernel@...r.kernel.org, 
	amd-gfx@...ts.freedesktop.org, spasswolf@....de
Subject: Re: commit 7ffb791423c7 breaks steam game

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.

Bert Karwatzki