DSR and input lag

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hejonar
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DSR and input lag

Post by hejonar » 02 Nov 2019, 21:41

Hey, I have GTX1060 3GB and was wondering does DSR introduce input lag? I was into doing 4K, 0% smoothness into 1080p, the effect looks pretty good and it's probably much faster than normal 4K>1080p down sampling(that introduces heap of input lag) but I feel it has bit slower response than native 1080p. Is it me or does DSR introduce input lag?

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jorimt
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Re: DSR and input lag

Post by jorimt » 02 Nov 2019, 22:17

Short of 4k DSR possibly reducing your framerate and/or making your system GPU-bound where it may otherwise not be when at native 1080p, no, it shouldn't, but one factor that can make it feel like this, is that when you DSR 4k to 1080p, you're mouse is going to feel a lot slower due to a need for a higher DPI to reach an equivalent (1080p) sensitivity when using the now higher effective resolution.

E.g. The same DPI level progressively feels slower the higher the effective resolution; try upping it when using DSR.
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hejonar
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Re: DSR and input lag

Post by hejonar » 02 Nov 2019, 23:32

Hey, thanks for answer. The application is very CPU bound and bottlenecked, I was actually wondering how to get GPU to do some stuff as even with 4K DSR it's still in 50-60% usage range(10-30% in 1080p). Would DSR cause increased CPU usage too? As for mouse, would going from 1080p to 4K mean that I need to double my mouse DPI to get exact same speed? Finally, what is the difference between normal downscaling(forcing higher resolution on smaller monitor) and DSR? It seems to me that downscaling is adding very massive input lag while DSR is adding just a bit.

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jorimt
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Re: DSR and input lag

Post by jorimt » 03 Nov 2019, 08:41

hejonar wrote:Would DSR cause increased CPU usage too?
Since DSR increases resolution, it will increase all system usage across the board. But regarding the CPU in particular, typically, the higher the resolution, the higher the GPU usage, but if you're app isn't particularly demanding and/or is CPU bound, it's going to be harder to max out the GPU, regardless of how high you pump the settings or how high of an FPS your system reaches (e.g. CS:GO, etc).
hejonar wrote:As for mouse, would going from 1080p to 4K mean that I need to double my mouse DPI to get exact same speed?
Mathmatically, double, yes, but individual tolerances/perceptions will apply, so even if you use exactly double, the DPI may or may not feel exactly the same to you, so adjust as desired after using double as a baseline increase.
hejonar wrote:Finally, what is the difference between normal downscaling(forcing higher resolution on smaller monitor) and DSR? It seems to me that downscaling is adding very massive input lag while DSR is adding just a bit.
As far as I know, beyond not having to manually create a custom resolution (and the availability of the "Smoothness" setting), there is no real technical difference between the two, and other than downsampling causing reduced FPS/increased GPU usage and a need for a higher mouse DPI over native res, I've never heard of it causing more notable input lag.

Then again, I'm not a downsampling specialist, so perhaps someone else here will know more about that aspect in particular.
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hejonar
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Re: DSR and input lag

Post by hejonar » 03 Nov 2019, 13:36

The thing is, I can run it natively down-sampled in any refresh rate I want. It just feels sluggish. I forgot to add, I got in-game FPS limiter enabled, v-sync disabled and nvidia latency set to ultra when this happens.

Also, there are so many contradicting stories about DSR/downsampling and input lag that nothing is certain.

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jorimt
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Re: DSR and input lag

Post by jorimt » 03 Nov 2019, 14:33

hejonar wrote:The thing is, I can run it natively down-sampled in any refresh rate I want. It just feels sluggish.
Beyond the reasons I already stated, I'm not sure then.

The only other thing I can think of, is have you verified that it's utilizing your monitor's highest refresh rate in-game when using non-DSR downsampling? Because I have heard of cases where custom resolutions sometimes force a lower-than-max refresh rate in certain situations/games.

If not, that's all I got on the subject currently.
hejonar wrote:Also, there are so many contradicting stories about DSR/downsampling and input lag that nothing is certain.
That's true, and that's because virtually everyone who has discussed this is just guessing based on subjective experience; high speed tests (or similar) would have to be done to confirm whether downsampling is adding input lag over native res (for whatever reason).
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hejonar
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Re: DSR and input lag

Post by hejonar » 03 Nov 2019, 15:35

jorimt wrote:The only other thing I can think of, is have you verified that it's utilizing your monitor's highest refresh rate in-game when using non-DSR downsampling? Because I have heard of cases where custom resolutions sometimes force a lower-than-max refresh rate in certain situations/games.
The difference exists also when I am comparing it at default refresh rates. But of course it could be something else causing it.

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jorimt
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Re: DSR and input lag

Post by jorimt » 03 Nov 2019, 16:39

Then my previous comment stands:
high speed tests (or similar) would have to be done to confirm whether downsampling is adding input lag over native res (for whatever reason).
I'm sure if any other regulars here have something to say on the subject, they will...
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hejonar
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Re: DSR and input lag

Post by hejonar » 03 Nov 2019, 18:04

As of note, I also have that "input lag" feeling when using MSAA. In terms of "input lag" I would rate it: native>MSAA=DSR>downsampling

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