So, in the quest for the lowest latency in retrogaming, I installed Ubuntu 18.04 on a usb pendrive with the aim to use Retroarch in KMS mode. I have an old Radeon HD 6370M so the only option was the radeon open source driver.
With this setup, I was able to achieve next frame response with a moderately fast wired controller and a crt monitor connected through the VGA port of my notebook, however, because I mostly play NES and SNES, I wanted my monitor's refresh rate to match those systems as closely as possible (about 60.098813 Hz), so I tried three different superwide modelines:
- Modeline "2880x480@60" 100.76 2880 2912 3288 3320 480 490 495 505 (should be 60.09782 Hz)
- Modeline "2880x480@60" 108.17 2880 2952 3240 3600 480 483 493 500 (60.094 Hz)
- The same as 2 but with a dot clock of 108.18, which should give exactly 60.1 Hz)
The actual rates, as measured by Retroarch itself, are about:
- 60.067 Hz
- 60.154 Hz
- Mostly the same as 2.
I want to point out that hardware is NOT the problem here, as every one of the above modelines give EXACTLY the expected refresh rates under Windows 10, also, Retroarch is not the problem either, since I modified kmscube to give me the refresh rate it is running at, and it mostly matches what Retroarch is measuring.
Also, VSync has always been on (since I haven't even been able to disable it outside of X), and I tried to:
- disable the built-in monitor of my notebook;
- disable VSync, however that only works under X;
- disable dpm and enable dynclk in the kernel.
Nothing worked. The frequency is also correct, at 750 MHz for the core and 800 MHz for memory.
I know this may seem silly, but this is really driving me crazy, and the next step would be to try under Archlinux, but I don't know if it is worth the hassle, since the driver would be the same.
Thanks anyway.
EDIT: Ok, it's not Ubuntu nor the GPU driver, I now believe it's the kernel itself...
