NVIDIA Reflex Low Latency - How It Works & Why You Want To Use It

[jorimt]

I thought the additional option was intended for this purpose so that the graphics card still clocks high in a CPU-bound case.

Boost merely ensures the GPU stays at its max base clock speed or higher (aka doesn't downclock below base), which does not guarantee an increase in actual GPU usage at that clock speed.

[SvenL]

Boost merely ensures the GPU stays at its max base clock speed or higher (aka doesn't downclock below base), which does not guarantee an increase in actual GPU usage at that clock speed.

Ah ok, I see. Thanks

[TheKelz]

I've chosen to go with GSync + NVCP VSync + Reflex Boost (which limits FPS to 138) with this game, but I can still notice input lag compared to GSync and VSync off (but it becomes stuttery/jittery as well). Would putting FPS cap lower than 138 help with this input lag?

The only input latency difference between G-SYNC on + V-SYNC on + an FPS limit within the refresh rate and G-SYNC off + V-SYNC off is tearing; the former won't, the latter will.

Tearing artifacts are causing both the "stuttery/jittery" feel, as well as any slightly faster frame delivery due to those very tears in the G-SYNC off + V-SYNC off scenario. G-SYNC prevents tearing by dynamically steering the tearline off-screen.

If you're using G-SYNC on + NVCP V-SYNC on + Reflex Boost (the last of which is both preventing the framerate from exceeding the G-SYNC range, as well as any additional render queue latency [unrelated to G-SYNC operation] whenever the GPU is maxed), then it's as low latency a tear-free syncing method can get on a 144Hz monitor.

So no, a lower-than 138 FPS won't reduce latency further in your particular scenario. Any lower latency would require a higher max Hz (aka larger G-SYNC range) and/or tearing at that same Hz.

Thank you, will take a note. Also, just noticed I wrote "crap" instead of "cap" lol, edited.

[jorimt]

Also, just noticed I wrote "crap" instead of "cap" lol, edited.

Knew what you meant I've now edited it in the remaining quote instances for you regardless.

[jabbo]

Is the fps limit that Reflex applies (when Vsync+Gsync on) the same as the NVCP max frame rate limit? I know there are differences between RTSS limit, nvcp limit, and in-game limits, in terms of input latency, so I'm curious which is the lowest-latency method for limiting.

As an example. With OW2, If I enabled Reflex with my 175hz monitor it caps at 166 fps. Is that "fps limiter" function lower latency than setting an in-game cap to 166 vs RTSS at 166, vs NVCP 166? Or does reflex somehow set the limit without inducing frame limiter latency like the other methods do?

[jorimt]

Is the fps limit that Reflex applies (when Vsync+Gsync on) the same as the NVCP max frame rate limit?

I tested this very thing a while back. See:
viewtopic.php?f=5&t=9151&p=72211#p72182

Short answer: the Reflex limiter, unlike NVCP MFR or RTSS, appears to be implemented at the engine-level, and is thus as low latency as the in-game limiter.

[jabbo]

Great, thank you.

[BoredErica]

I have games that are CPU bound maybe 80% of the time and GPU bound 20% of the time. Should I just enable Reflex if game supports it just in case it helps? I think the answer hinges on whether Reflex has any negative side effects. I heard ULLM can increase stutters when CPU can't keep up. Same idea here?

[jorimt]

I have games that are CPU bound maybe 80% of the time and GPU bound 20% of the time. Should I just enable Reflex if game supports it just in case it helps? I think the answer hinges on whether Reflex has any negative side effects. I heard ULLM can increase stutters when CPU can't keep up. Same idea here?

Unlike ULLM, Reflex doesn't actually adjust the amount or timing of pre-rendered frames in the render queue (which can cause stutter), but instead monitors whether the GPU usage is maxed.

If/when it is, Reflex sets a dynamic engine-level framerate limit slightly below the currently sustainable average framerate as to prevent the GPU from maxing, which eliminates extra pre-rendered frame creation caused by GPU-bound scenarios.

[Patryk]

Does anyone know how I can fix Reflex + VSync + ULLM locking frames to 225? I expected it to jump to at least 260 fps when I changed monitors, but it seems to be stuck at 225 from previous 240Hz monitor. I've tried switching each option on/off, but that didn't change anything. Am I forced to play without V-Sync and lock my frames manually now? I quite enjoyed the automatic fps cap before.