FPS limiter introduces lots of input lag

[Bel]

A Reddit user did some measurements to check the resulting input lag when using various Steam FPS caps:

https://www.reddit.com/r/SteamDeck/comments/ug9kc2/psa_enabling_the_framerate_limiter_adds/?utm_medium=android_app&utm_source=share


Upcapped: 31.8ms
60fps cap: 75.8ms
30fps cap: 145.9ms
50hz/uncapped: 32.5ms
50hz/50fps cap: 94.2ms
50hz/25fps cap: 186.1ms
40hz/uncapped: 34.3ms
40hz/40fps cap: 121.1ms
40hz/20fps cap: 232.0ms

If possible, it would be nice if the input lag could be lowered a bit without giving up the consistent frame times the limiter currently has.

[christofin]

This has to be due to the triple buffered VSync implementation, right?

I think even with double buffering there would be a lot of input lag. Still, this would be something that would be nice to have as a feature.

Or even have some sort of "scanline sync" option for users who want to turn off VSync so that they can control where the tearing with VSync off occurs for best image quality and least input lag.

Valve could probably be creative and come up with novel ways to reduce input lag. It is pretty oof with the 30fps limiter at the moment. I get less input lag running games at 60fps and streaming over WiFi from my gaming PC....

[PlayerOne]

That´s just how VSYNC works and alway has been.
If you want low input lag disable VSYNC (make it uncapped) and use ingame frame limiters.

[Bel]

Originally posted by christofin:

This has to be due to the triple buffered VSync implementation, right?

I think even with double buffering there would be a lot of input lag. Still, this would be something that would be nice to have as a feature.

Or even have some sort of "scanline sync" option for users who want to turn off VSync so that they can control where the tearing with VSync off occurs for best image quality and least input lag.

Valve could probably be creative and come up with novel ways to reduce input lag. It is pretty oof with the 30fps limiter at the moment. I get less input lag running games at 60fps and streaming over WiFi from my gaming PC....

If they could do something like Scanline Sync and reliably move the tear-line off-screen, that could be a pretty awesome fix if it keeps latency down.

I heard something along the lines of Gamescope (or other Linux compositiors) being able to cut out tearing by default (at the cost of latency) , and there are actually some efforts to get tearing back in as an option for better latency.

[AstroAss]

This is something I distinctly noticed the other day when I picked up my Steam Deck after an update to play Diablo II: Resurrected. I use the trackpads to do the inventory management and noticed that for some reason my mouse cursor is now all "soupy", lagging behind me and I end up overshooting with my thumb.

This has to be recent, rather than the way it's always been.

[Dreambox]

bumping because this is a big issue that needs to be adressed asap

Originally posted by PlayerOne:

That´s just how VSYNC works and alway has been.
If you want low input lag disable VSYNC (make it uncapped) and use ingame frame limiters.

No, you'll never get that much latency with your PC or console, with or without vsync, 145.9ms at 30 FPS is incredibly high

[retrogunner]

OP - That post sounds like something you share with The Phawx on YT. I've not heard him mention anything about input lag in his exploration of the 40/40 limits.

[Vitameanslife]

So basically the framecaps are just completely unusable?

[Byron]

Originally posted by Vitameanslife:

So basically the framecaps are just completely unusable?

Seems to vary by game. Played Lego Undercover locked to 40 and no way is input lag as bad as that - other games seem to be though.

[christofin]

Originally posted by Vitameanslife:

So basically the framecaps are just completely unusable?

I got through 2 major bosses in Elden Ring on my Deck with the 30fps cap, so it's definitely "usable" - though it would be great if Valve could find ways to reduce input lag still.

[Prime Rib]

Just want to give support to this post so Valve can see it, they are most likely highly aware but now the community has found it, it's something we need addressed at some point.

[retrogunner]

OP - as Vulture posted - to get Valve's awareness, you might consider moving this or posting your metrics to the Bug sub-forum of this discussion area. It would likely be helpful to include the games used for testing as well.

[BluesyMoo]

Just a general idea regarding vsync: wouldn't it be possible to update to a new frame in random / interleaved scanline order? This way, if vsync is off, there will not be a split that's clearly visible.

Or update individual pixels in random order.

[inFantry-32]

Originally posted by PlayerOne:

That´s just how VSYNC works and alway has been.
If you want low input lag disable VSYNC (make it uncapped) and use in-game frame limiters.

Use in-game?

Not every game has a limiter and even then some of those are actual garbage.

Valve just needs to expand V-SYNC options for advanced users, like choosing your level of buffering or to disable V-Sync while using the limiter separate.

Although I think they should keep it there by default, as most people would complain otherwise about tearing constantly & this is the lesser of two evils.

[inFantry-32]

Originally posted by Dreambox:

bumping because this is a big issue that needs to be adressed asap

Originally posted by PlayerOne:

That´s just how VSYNC works and alway has been.
If you want low input lag disable VSYNC (make it uncapped) and use ingame frame limiters.

No, you'll never get that much latency with your PC or console, with or without vsync, 145.9ms at 30 FPS is incredibly high

Agreed.