On 9/22/26 10:50 AM, Leo Li wrote:
>
>
> On 2026-09-21 15:47, Matthew Schwartz wrote:
>> Hi George,
>>
>> After updating to Linux 7.2.x, I noticed gamescope's frame limiter falling
>> below the requested rate. The reproducer was a Navi 33 driving 4K120
>> through a DP-HDMI PCON, with VRR disabled. A 40fps limit was producing
>> roughly 37fps.
>>
>> Gamescope was pacing against the fixed 120Hz refresh interval, but we
>> observed frame intervals stretching to around 9.34ms instead of 8.33ms.
>> The OTG vtotal also increased from 2249 to 2521. This was enough to
>> disrupt the limiter's pacing despite userspace leaving VRR_ENABLED=0.
>
> Hi Matt,
>
> I wonder if this has to do with re-introducing 2-frame vblank off for NV3+
> DGPUs, which made it into 7.2:
>
> fba211b078d6 ("Revert "drm/amd/display: Restore 5s vbl offdelay for NV3x+
> DGPUs"")
>
> Since gamescope is only updating every 3rd frame, it's possible vblanks were
> turned off during those two frames, signaling driver to enable idle
> optimizations.
>
> To test this idea, does bumping this line to something like 5 frames ((u64)50
> *) help?
> https://elixir.bootlin.com/linux/v7.3-rc3/source/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c#L3377
Tested this by reverting my own patch in the kernel and replacing it with this,
and unfortunately the issue
still reproduces here. In Hades 2, a 40FPS limit is locking to 37FPS
erroneously.
Matt
>
> Thanks,
> Leo
>>
>> Tracing this led to allow_freesync remaining true for a VRR-capable
>> sink even when the FreeSync state was inactive. That allowed FPO to
>> stretch vblank around UCLK switches. The PCON whitelist change exposed
>> this on our setup by making the sink eligible for that path.
>>
>> The intent is to keep the frame period fixed when userspace has
>> disabled VRR, while retaining FPO eligibility when variable refresh is
>> actually requested. With the patch, the original setup holds the
>> requested 40fps again. I also tested VRR toggling on a Legion Go 2's
>> internal eDP OLED panel and did not observe a regression.
>>
>> Thanks,
>> Matt
>
