Weird visual glitch on 3D psx games when using runahead with 2+ frames

[TDS]

I get this weird visual glitch on 3D PSX games when using 2 or more frames for run ahead on beetle psx (software or HW in software mode). Random colored triangles start to blink fast on top of the games textures, usually on the ground, either when the camera is moved or in some very specific angles. Only happens with 2 or more frames for run ahead, 1 or off is fine. Seems to get worse in both size and frequency the more frames above 2 I try. Tested with glcore and vulkan renderers, same results. Running Retroarch 1.9.5, gtx 1660 super, i5 2500k OC’ed, win10 pro. I vaguely remember a similar issue when running the same games on my old gtx 760 as well. Example below from Shadow Tower, but I remember Threads of Fate also having the same issue.

Example with 2 frames:

Examples with 3 frames:

[hunterk]

Runahead (and rollback netplay) are incompatible with hardware-rendered cores because the hardware contexts can’t handle the state hopping around so much. I haven’t seen this particular issue before, but it’s probably related to that.

[TDS]

Isn’t Beetle PSX (the non HW one) software-rendered tho? I always thought runahead wouldn’t even work at all on hardware rendering.

[hunterk]

correct. If you’re using the software-renderer, it should be okay, though you may also need to disable the dynarec.

[TDS]

Trying with Interpreter instead of Dynarec, except for the worse performance, the visual glitches are the same. I tried testing on beelte psx HW with the renderer set to software, same exact behavior as the software only core. I wonder if it’s something with my setup? I would imagine something like this would attract attention if it was widespread. If anyone has any idea or knowledge I could use to troubleshoot, would be greatly appreciated.

[hunterk]

Hmm, dunno. do you have any PGXP options enabled?

[TDS]

Nah, I’m running everything on default beetle psx settings except for dynarec, which I already tried setting to interpreter. I tried turning on PGXP just to see what happens, and instead of those small triangles, I get big stretched 2d shapes much larger and seemingly “floating” instead of being on top of the floor texture, also blinking. These also only happen if runahead is set to 2 or more. At 1 or off, PGXP works just fine.

[hunterk]

Interesting. I’m stumped

[Awakened]

Might want to try the Duckstation core’s internal run ahead core option and see if it works better.

[TDS]

I didn’t know duckstation had a internal runahead. It worked fine, I get about the same performance as beetle psx with 2 frames without any glitches on shadow tower. Thanks!