An input lag investigation

RetroArch General
#802

It depends on how resource intensive the core is and game you’re playing.

For me I have an i5 4670k not oc’ed and GTX 770 and spent a good day off going through all the cores I use and obtained a general idea of what my machine can and can’t handle.

Using the OGL backend For example systems up until say PSX my machine can handle GPU hard sync 0, frame delay of 10 and run ahead of 2 frames (could handle even more frames but then the game starts to glitch) Using Game mode on my Plasma and DS4 Bluetooth connnection (4ms polling rate) I can’t tell the difference between my CRT and my Plasma with input lag. After PSX I cannot handle run ahead that well but I can get away with shaving off some lag with frame delay.

#803

But what about vulkan vs opengl for hardware intensive cores?

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#804

I’ve never felt compelled to Use Vulkan because OGL has done the job for me so there I can’t really help you.

#805

Some cores can’t be helped with whatever options you can throw at them. Mednafen Saturn and the more recent PPSSPP updates are the worst offenders. Same with some N64 games that use framebuffer. That’s more than 4 full frames of lag on top of any other lag from the LCD, etc. GPU sync, frame delay, etc barely do anything.

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#806

could you test the other input methods for the 8bitdo sfc30? I was under the impression that the xbox mode (x then turn on)of the control was faster than the d-input (turn on without pressing any extra button) one when conected over cable.

#807

doesn’t mednafen saturn have have midframe input sync option to reduce input lag?

#808

Yeah but it makes no difference. At least on the core/my system.

#809

You probably have the equivalent of that playing with the “frame delay” value.
But that’s still really stressful on the cpu anyway.

#810

Does enabling rewind increase the input lag?

#811

Enabling rewind adds a savestate to every frame, which increases processing time by a very small amount. Saving state is usually far less work than emulating a frame.

It’s so insignificant that it only matters for people who are using the Frame Delay feature, and might need to turn that down a notch.

#812

Processing time as in additional input lag or additional cpu usage? I’m aware that it increases the cpu requirements for a core but didn’t know if it increased input latency.

#813

Rewind does have a significant performance hit though. It may depend on how the savestate code is implemented in each core I guess.

#814

If you’re using frame delay, at worst, rewind is going to cost you a couple of milliseconds for most cores (i.e., you might only get up to frame delay 8 instead of 10 or whatever). So, that’s a couple more milliseconds of latency. If you’re not using frame delay, there won’t be any increase at all.

#815

How does it impact run ahead?

#816

It shouldn’t have any effect at all, as both rewind and runahead require taking states on each frame.

#817

Does using either gsync or freesync decrease input lag? I know that in traditional pc games, using either helps to eliminate most of regular vsync lag.

edit: Wow, using scan line sync from RTSS with SSF brings the input lag below beetle saturn + vulkan. Also am not noticing any tearing or stuttering. Hopefully retroarch can get that some day.

1 Like
#818

Hello Brunis, thank you for all your work on input lag, it is very thorough. Do you own any arcade/fight sticks that you could possibly do any input lag testing on? Really interested to know how the 8bitdo N30 arcade stick stacks up to other sticks like Qanba, Hori, Brooks, etc.

#819

Sorry, I only own a bunch of gamepads, no arcade controls.

#820

This guy on Facebook solved it,maybe you can use his “data” instead?

“Anthony Ball lol. Maximum input lag on a 60hz SNES games is 16ms. Your game is displayed and on the next vblank you process the previous grab from the controller. So if you run at 60hz then the delay from gab to processing is less than 1/60 sec. 1/60 sec is 16ms. I don’t remember any games on the SNES that didn’t run at 60hz.”

#821

LOL indeed… :stuck_out_tongue: