[Bug 2069380] Re: FPS of glxgear with fullscreen is too low on MTL platform

** Tags added: jira-somerville-37

** Tags added: somerville

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https://bugs.launchpad.net/bugs/2069380

Title:
FPS of glxgear with fullscreen is too low on MTL platform

Status in linux package in Ubuntu:
Invalid
Status in linux-oem-6.8 package in Ubuntu:
Invalid
Status in linux source package in Noble:
In Progress
Status in linux-oem-6.8 source package in Noble:
In Progress

Bug description:
[Impact]
Run `glxgears -fullscreen` and the FPS can't stay at 60 FPS
298 frames in 5.0 seconds = 59.465 FPS
241 frames in 5.0 seconds = 48.193 FPS
261 frames in 5.0 seconds = 52.030 FPS
268 frames in 5.0 seconds = 53.596 FPS

[Fix]
Bisect the kernel and found a commit in v6.9-rc1 fixes the issue
c08c364102d0 drm/i915: Bypass LMEMBAR/GTTMMADR for MTL stolen memory access

[Test]
1. Run `glxgears -fullscreen` on MTL platforms
2. The FPS should be always around 60

[Where problems could occur]
It's a workaround only affects MTL platforms, and there is no "fixed commit" for this patch after v6.9-rc1. So, it should be safe and essential for MTL platforms.

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