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

Everything about latency. Tips, testing methods, mouse lag, display lag, game engine lag, network lag, whole input lag chain, VSYNC OFF vs VSYNC ON, and more! Input Lag Articles on Blur Busters.
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jorimt
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NVIDIA Reflex Low Latency - How It Works & Why You Want To Use It

Post by jorimt » 19 Sep 2020, 07:50

I've recently had a few users asking me about this setting and it's relation to G-SYNC in the comments section of the G-SYNC 101 article.

To sum-up, it's not directly related to G-SYNC operation (the operation of which primarily occurs between GPU and Display), but instead to the pre-rendered frames queue (which occurs between CPU and GPU); e.g. Low Latency Mode (formerly known as "Maximum Pre-rendered frames" in the NVCP).

Battle(non)sense has released an explainer video with tests:

phpBB [video]


To sum-up:

1. For games that support Reflex, LLM and Reflex can be stacked, but LLM will have no further beneficial effect in this case, and can be disabled.
2. Reflex "On" = (true) MPRF "0" (even in GPU bound scenarios), Reflex "On + Boost" = (true) MPRF "0" (even in GPU bound scenarios) + Power Management Mode "Prefer Maximum Performance."
3. Reflex eliminates the pre-rendered frames queue, but it does not prevent sync-induced input lag or keep G-SYNC in range, thus a minimum -3 FPS limit (be it external or internal) is still required to remain in the G-SYNC range. Same goes for low lag V-SYNC; an FPS limiter is still required. EDIT: With G-SYNC + NVCP V-SYNC + Reflex, it has been suggested in Nvidia documentation that Reflex behaves like LLM "Ultra" in that it sets an auto FPS limit slightly below the refresh rate. Once I've had a chance to more fully test Reflex myself, I'll ultimately amend my optimal G-SYNC setting (https://blurbusters.com/gsync/gsync101- ... ttings/14/) with general information and recommendations (below the existing LLM section) for Reflex configuration when used with G-SYNC.

========

Update #1 (10/03/2020):
I've now tested and verified base Reflex functionality in Call of Duty: Warzone, Fortnite, and Valorant...

Specs
  • Nvidia Driver 456.71
  • XB271HU (144Hz native G-SYNC)
  • 1080 Ti
G-SYNC on + NVCP V-SYNC on + in-game V-SYNC on OR off + Reflex ("On" or "On + Boost")
  • Reflex applies an automatic FPS limit slightly below the refresh rate. At 144Hz, it limits to ~138 FPS, just as LLM "Ultra" (in supported games) did before it. This auto FPS limit is relative to the current maximum refresh rate.
  • If an in-game or external FPS limiter is to be used with Reflex enabled, the in-game or external limiter must set slightly below Reflex's automatic limit for it to override Reflex's. This will not override Reflex's auto FPS limiting function (and thus, render queue elimination benefits) when the game is GPU-bound and frames are fluctuating, and will instead only override the initial static Reflex FPS limit where the game is not GPU-bound and the system can maintain a framerate that could otherwise exceed the limiters if they were disabled.
G-SYNC on OR off + NVCP V-SYNC off OR "Use 3D application setting" + in-game V-SYNC on OR off + Reflex ("On" or "On + Boost")
  • Reflex does not apply an automatic FPS limit slightly below the refresh rate, but retains all other functionality.
(jorimt: /jor-uhm-tee/)
Author: Blur Busters "G-SYNC 101" Series

Displays: Acer Predator XB271HU / LG 48CX OS: Windows 10 MB: ASUS ROG Maximus X Hero CPU: i7-8700k GPU: EVGA RTX 3080 FTW3 UG RAM: 32GB G.SKILL TridentZ @3200MHz

Simon95
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Re: NVIDIA Reflex Low Latency - How It Works & Why You Want To Use It

Post by Simon95 » 19 Sep 2020, 08:41

When I already cap my frame at stable FPS (80% GPU Load). Will there be any input lag improvement with NVIDIA Reflex?

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

Post by jorimt » 19 Sep 2020, 08:53

Simon95 wrote:
19 Sep 2020, 08:41
When I already cap my frame at stable FPS (80% GPU Load). Will there be any input lag improvement with NVIDIA Reflex?
Going by Battle(non)sense's results (~7:06 timestamp here: https://youtu.be/QzmoLJwS6eQ?t=426), for games that support Reflex, you no longer need to cap your FPS to a level that prevents max GPU usage, at least for the direct purpose of preventing additional input lag from the pre-rendered frames queue.

Instead, you only need to cap your FPS to keep syncing methods such as G-SYNC in range, or to maintain a steadier average framerate for consistency reasons. Reflex will take care of the additional input lag introduced by the render queue when the GPU is maxed.
(jorimt: /jor-uhm-tee/)
Author: Blur Busters "G-SYNC 101" Series

Displays: Acer Predator XB271HU / LG 48CX OS: Windows 10 MB: ASUS ROG Maximus X Hero CPU: i7-8700k GPU: EVGA RTX 3080 FTW3 UG RAM: 32GB G.SKILL TridentZ @3200MHz

howiec
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Joined: 17 Jun 2014, 15:36

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

Post by howiec » 21 Sep 2020, 05:30

Finally, no more wasted frames from using an in-game FPS cap.

I'm curious to see if this helps with mouse sensitivity/feel issues with Apex Legends when FPS fluctuates, although I doubt it.
I'm guessing it's just an old engine and some sub-optimal Respawn coding.

andrelip
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Joined: 21 Mar 2014, 17:50

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

Post by andrelip » 24 Sep 2020, 11:09

howiec wrote:
21 Sep 2020, 05:30
Finally, no more wasted frames from using an in-game FPS cap.

I'm curious to see if this helps with mouse sensitivity/feel issues with Apex Legends when FPS fluctuates, although I doubt it.
I'm guessing it's just an old engine and some sub-optimal Respawn coding.
The short answer is "it depends".

When the GPU usage is high (50%+), you have a distribution of frames where a small percentage is probably slower in the GPU than the CPU. It will lead to a short queue that could be accumulating. For those cases, Reflex will help. Nvidia Frametime is your friend; plot the Queue Depth, and look the distribution for values above 1.

The rendering queue usually has the most significant latency, but you could also feel the latency just by an increase in the CPU or GPU time. In those cases, Reflex will do nothing.

In CPU bound games, you can also have latency by power savings as GPU is idling too much. I suggest fixing the clock using Afterburn and setting maximum performance in the Nvidia settings for your game and "DWM" and "explorer" as those usually override the Global Settings. For this case, "Reflex + Boost" option will help.

Finally, you can also have latency due to thermal throttling. Try to fix the frequency or even underclock a little to a value that your system can sustain.

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

Post by xensid » 24 Sep 2020, 23:06

I suggest fixing the clock using Afterburn
What do you mean by fixing the clock?

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

Post by andrelip » 26 Sep 2020, 09:39

xensid wrote:
24 Sep 2020, 23:06
I suggest fixing the clock using Afterburn
What do you mean by fixing the clock?
1: Press [CTRL + F] to open the curve.
2: Select a point in the curve with a stable value.
3: Press [CTRL + L], a vertical line should appear. Then close the window.
4: In the Afterburn menu, click the ✅symbol.

disq
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Joined: 10 Oct 2018, 16:05

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

Post by disq » 26 Sep 2020, 11:08

phpBB [video]

blackstorm82
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Re: NVIDIA Reflex Low Latency - How It Works & Why You Want To Use It

Post by blackstorm82 » 02 Oct 2020, 12:15

jorimt wrote:
19 Sep 2020, 08:53
Simon95 wrote:
19 Sep 2020, 08:41
When I already cap my frame at stable FPS (80% GPU Load). Will there be any input lag improvement with NVIDIA Reflex?
Going by Battle(non)sense's results (~7:06 timestamp here: https://youtu.be/QzmoLJwS6eQ?t=426), for games that support Reflex, you no longer need to cap your FPS to a level that prevents max GPU usage, at least for the direct purpose of preventing additional input lag from the pre-rendered frames queue.

Instead, you only need to cap your FPS to keep syncing methods such as G-SYNC in range, or to maintain a steadier average framerate for consistency reasons. Reflex will take care of the additional input lag introduced by the render queue when the GPU is maxed.

If it's not bound to the gpu, is it correct that the reflex doesn't work either?
-------------------------------
[144HZ]
GSYNC ON + VSYNC OFF
141 FPS CAP GPU 50%-70%
REFLEX ON+BOOST
-------------------------------
Reflex doesn't help in this situation, right?

----------------------------------------------------
[144HZ]
GSYNC ON + VSYNC OFF
280 FPS [NOT CAP] GPU 95-99%
REFLEX ON+BOOST
95-99% Is it only turned on with a similar behavior to the low-latency mode?

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

Post by jorimt » 02 Oct 2020, 12:30

blackstorm82 wrote:
02 Oct 2020, 12:15
If it's not bound to the gpu, is it correct that the reflex doesn't work either?
Reflex eliminates the render queue. In GPU-bound situations, the render queue becomes saturated. In non-GPU-bound situations, the render queue is typically already near empty or empty.
blackstorm82 wrote:
02 Oct 2020, 12:15
[144HZ]
GSYNC ON + VSYNC OFF
141 FPS CAP GPU 50%-70%
REFLEX ON+BOOST
-------------------------------
Reflex doesn't help in this situation, right?
Right.
blackstorm82 wrote:
02 Oct 2020, 12:15
[144HZ]
GSYNC ON + VSYNC OFF
280 FPS [NOT CAP] GPU 95-99%
REFLEX ON+BOOST
95-99% Is it only turned on with a similar behavior to the low-latency mode?
When enabled, Reflex is "turned on" whether your system is GPU-bound or not. But since it removes the render queue, how much it reduces input lag depends on how full your render queue would be if Reflex was not enabled.

Reflex is a replacement to LLM. LLM only reduces the render queue. Reflex removes it.
(jorimt: /jor-uhm-tee/)
Author: Blur Busters "G-SYNC 101" Series

Displays: Acer Predator XB271HU / LG 48CX OS: Windows 10 MB: ASUS ROG Maximus X Hero CPU: i7-8700k GPU: EVGA RTX 3080 FTW3 UG RAM: 32GB G.SKILL TridentZ @3200MHz

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