Input lag, subective and sensitive subject :-)

RetroArch General
#1

Hi everyone !!

I would love to have your opinion on this dreaded subject… input lag !

Some people do not notice it at all. Some like me are obsessed with it !

More generally, on my 2 setups (Kubuntu Linux + retroarch ; Raspberry Pi 2 + Happi Game Center or Lakka) I definitely feel a slight input delay. Sometimes it is just barely noticeable. Sometimes I feel it makes me bad at games (i.e. : manic shooters).

I made many tests with different screens, software settings, emulators, joysticks, arcade panels etc etc. and it’s always more or less the same. I remember I used to feel none on my old PC with PS/2 ports but maybe I was less focused on this at that time (it was a Linux machine too, under Kubuntu).

When I compare to the originals (i.e. the same game on the original machine ; I have an Amiga, Dreamcast etc.), I feel NO input delay at all and find the games more enjoyable.

What do you think ? What is it due to ? Could it be eventually improved ?

I guess some factors are…

  • libsdl ?
  • the Linux kernel ? the USB stack ?
  • some retroarch cores ?
  • screen (post processing)

Maybe it could be improved, for instance on the Raspberry, when using the GPIO.

I thought CPU speed could play but I tried with much faster machines (i3, i5) and I always see some kind of input delay. I’m unable to measure it, unfortunately, but I guess that what matters is the subjective feeling and its consequence on the gameplay.

Well, I’d love your opinion !

#2

Lots of input lag come from the TV settings. All the filters make input lag. SomeTV have a “game mode” (samsung) to stop all filters and there isn’t any lag anymore regards

#3

Some amount of latency with emulation is completely unavoidable. USB polling is a small contributor of approx. half of a frame and while PS/2 stream protocol (or GPIO) could theoretically provide less latency, the way emulators poll for input renders it moot. Post-processing can be a significant issue, depending on the shader/filter used (if any). I haven’t tested whether RA’s overlays add any latency or not. SNES cores seem to have some built-in latency that’s not there on, for example, genesis cores. There may be other cores in the same boat. In my testing, those SNES cores had the same latency running standalone vs RetroArch, and the fact that all SNES emus had it suggests that it’s something inherent to the SNES design and/or emulation thereof.

The BYOAC/GroovyMAME guys claim to achieve next-frame latency in Win7 64-bit but I haven’t had an opportunity to reproduce it. The best “feel” I’ve had with RetroArch is in KMS mode with audio latency turned down as far as possible. In Windows, you can turn on hard GPU sync 0, which is like an automatic version of GroovyMAME’s “frame delay” option (we also have frame delay, if that’s a thing you want to mess with; increase it until you get audio crackles on a per-game basis). There is also a new input polling option in settings > input called “poll type behavior” that may help when set to “late” vs “early” or “normal”. I haven’t gotten to do any extensive testing with that option, though, to determine whether the benefits others have perceived may be placebo effect.

#4

Oops, I didn’t see your reply, thanks a lot… Meanwhile, this thread took off, which makes me very happy :slight_smile:

http://libretro.com/forums/showthread.php?t=5428

#5

[QUOTE=Srk15372;33993]Lots of input lag come from the TV settings. All the filters make input lag. SomeTV have a “game mode” (samsung) to stop all filters and there isn’t any lag anymore regards[/QUOTE]

I have a Samsung TV and even with Game Mode enabled, there is still lag (less, but still there).

#6

I agree. Same setup with Samsung TV in game mode. To be fair, older versions of RetroArch (like over half a year ago) didn’t have this problem or it was a lot less pronounced. But there’s another thread investigating input lag.