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Comment by Aurornis | Hacker News Reader

With the exception of XWayland, all of the tests had input latencies within a very small range. No human could tell them apart by those latency differences alone. I would be amazed if someone could notice the 3ms difference jump to XWayland.

The difference could be much larger on a slower monitor. However the differences between Wayland and X11 as protocols is negligible. XWayland as an implementation looks to have a limitation.

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The context here is the article's author is a twitchy FPS player, those extra 3ms are something that community agonizes over. I appreciated how much effort was put into controlling the variables in this test. There's a whole lot of witchcraft associated with these kinds of efforts and he sat down and did the measurements and got real numbers. My hat is off to OP.

ping is going to dominate over 3ms in pretty much every situation.

And the non-xwayland numbers are all within a single ms of each other.

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Not to undermine the measurements of the author (agree with you, it's a cool effort), but my read is that this was basically proof that it doesn't matter.

It doesn't matter. Whether you have a ping of 40 or a ping of 300, 3ms is 3ms and will mean you win a little less often.

The saying we have in bike racing marginal gains is "leave no stone unturned, but turn over the big ones first"

So sure, first make sure your internet connection is solid. Then make sure your hardware and game settings are optimizing FPS to a reasonable point of diminishing returns.

Then make sure you don't use XWayland

You can genuinely feel just a few milliseconds of input latency with a mouse, it disconnects looking around with your physical actions. It's the same way you can feel the difference between low and high refresh rate monitors, even though you can't really count the frames themselves

In the context of competitive online games, ping is going to be ~10-60ms, depending on your connection to the particular server you're playing on, and not particularly noisy (and that's a roundtrip time. Client-Server latency would be 5-30ms). In order for one value to "dominate over" another in an adversarial context, the variance of the former must be much greater than the base rate of the latter.

Imagine a game that's just a pistol duel. When the kerchief hits the ground, players press a button, first person to press the button wins.

In an ideal world, with no delay whatsover, the probability P(A) of player A shooting no later than player B is 100 (because both players shoot at exactly the same time). If we add 5 ms of delay to player A, then P(A) = 0 (he will always lose). If then we add 50 ms of network latency to both players, P(A) = 0 still, because 55 > 50. If we instead make that 50ms delay 50ms +- 10ms (ignoring normal distribution for the moment, pretending every value in that range is equally likely), there's a 25% chance of player A experiencing an unwinnable delay (any network delay value > 55ms results in a value greater than player B's max of 60ms), resulting in a probability of P(A) = 75% * 50* = 38%.

If we make the network delay 50ms +- 5ms, then P(A) drops to 25%.

Since 4ms is already about at the limit of my input latency tolerance for snappiness, I came to a different conclusion: "Wayland VRR" is the only tolerable Wayland option.

Lag compensation means ping is an entirely different phenomena with different effects from input latency. While details vary between games for the most part pieces of the game like hitting enemies (but not being hit yourself) and moving your own character are operating on a local simulation with zero latency from ping.

There are weird consequences of this, someone can shoot you after you duck behind a wall because you hadn't yet in their version of the game. An enemy moving left right repeatedly is likely vibrating in your version of the game faster than the rules of the game would otherwise allow. Etc. Ping matters, but it's not comparable to input latency. Input latency really does mean that you can click at the right time and miss your enemy. It really does delay how fast your camera spins when you move your mouse. Etc.

Latency is additive, it doesn't matter how much latency you already have, any extra on top always still hurts.

I have no idea about gaming but in the music world you start noticing latency when it is above 5ms and the difference between 5 and 8ms is tangible. For the most part anything under 10ms is workable and you will quickly adapt as long as the latency is constant. Under 10ms of latency is a level of latency we are used to dealing with, if you are playing guitar and your amp is 10 feet from you, you have ~9ms of latency. Our brains are pretty good at adapting to these short latencies as long as they are predictable.

The visual latency on gaming could be different but I suspect not, I think it is more an issue that some people fixate on the latency, others just accept and adapt to it. Games do have more possible sources of latency, visual, audio and io, and if these can all be different that can be difficult; years ago I had an issue with this and midi, that one really threw me off. Games may also not model the physics of sound? does sound travel slower than light in games? That could worsen the problem since sound does travel slower in real life and we are used to that, we expect it.

It's very valuable data that everything is so close. It means that most folks can simply ignore it. On the other hand the inferior nature of xwayland well explains the bad rep for wayland latency.

Consider also that people neither run the latest thing nor the fastest software and remember potholes long after they are filled. EG it wasn't that long ago that wine was running on xwayland almost exclusively for instance and the majority of popular titles run via wine.

Also the author is testing a game engine.

It’s possible that Gnome/KDE/whatever has wildly different latencies on X11 vs Wayland.

I’d be interested in seeing that test.

But it’s great to know the difference is so small here, which is what I’d expect.

I can tell down to about a 3ms difference in lag. Actually even down to 1ms, it's not all its cracked up to be, lemme tell you.

You think you can and will inevitably fail to do it in blind testing.

While reaction response is around 100ms, for predictive movements, ie press a button exactly when a bouncing ball hits the ground, average people can get down into 5-7ms of timing accuracy[1]. Trained people can get below 4ms in certain cases.

Of course, the brain adapts. I played an online shooter at >100 FPS using my 144 Hz monitor (when that was the best). I visited a buddy who's PC could only muster 30-40 FPS, and he asked me to show me how I played, since he struggled.

I sucked so bad due to the extra input lag. Felt like my character was running in a pool of molasses. But after about 15-20 minutes my body adapted, and my performance started increasing and my hits started connecting more reliably. I got to about 90% of my regular performance after 30 or so minutes.

So while one could tell back to back, one could also compensate. But at some point the extra input lag will matter, and will get you killed or make you miss that shot. Hence why I could only get up to ~90% of my normal performance on my buddy's PC.

[1]: https://jov.arvojournals.org/article.aspx?articleid=2213289

Well, of course people can generally see the difference between 30 and 100+ FPS but it is much bigger delay than 1ms OP claimed they can distinguish.

As noted in the paper I linked to, display framerate did not affect the timing precision of their participants, from 120Hz down to 24Hz. So it's more about feeling it rather than seeing it.

If you can be accurate to below 5ms, an additional millisecond of input lag makes a big difference.

That paper measures our margin of error when syncing to a perfectly predictable rhythm, not our ability to detect system latency. Applying that to an FPS doesn't really work for two reasons. First, enemies are erratic, meaning you are mostly relying on your reactive visual-motor pipeline, which is bottlenecked by ~150ms anyway. Second, even for purely predictive shots, your brain subconsciously calibrates out fixed hardware lag.

I'll concede that pure prediction absolutely exists in FPS games-like tracking a falling player with the LG in Quake 3 or landing a predictive mid-air rocket. In such cases smoothness of high FPS helps, but adding a 1ms drawing delay to those 500FPS (what the article is about) won't be noticeable at all because your brain naturally calibrates out constant hardware delay.

It only calibrates it out over time, that was what my 100+ FPS to 30 FPS story was about.

So yes I agree over time you wouldn't be able to tell 1 ms from 2 ms, but a skilled player doing back to back comparisons might be very different.

Well, I don't think this is the case and I haven't seen any research to convince me otherwise.

I can tell, doesn't mean I can react usually.

Adapting is doable, but after years of rhythm games, yeah, no.

It directly impacts performance when playing twitch fps games, any input lag causes measurable difference in score. This is before people even notice it happening.

I would love to see some research confirming that 1ms of addition latency that OP claims to be able to perceive impact performance of twitchy FPS players.

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