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SLI input lag questions

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SLI input lag questions

Postby vabellabel » 10 Jun 2018, 05:06

Hi all,

I have 1080ti x 2. I am playing overwatch and am concerned about the small input lag SLI is causing. I will like to check which of the following will give me the lowest input lag.

1. Removing one card from motherboard

2. Disabling SLI completely in nvidia control panel

3. is 1 and 2 the same thing? Reason is I still see the gpu clock at 130++ mhz at evga xoc software after disabling SLI in nvidia control panel, which means it is still being used?

4. Selecting 'single gpu mode' in overwatch nvidia control panel settings

Thank you!
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Re: SLI input lag questions

Postby Chief Blur Buster » 10 Jun 2018, 15:48

The input lag of SLI depends on the game and how it is configured.

In certain scenarios -- it's the input lag of half the frame rate (e.g. 200fps with the input lag of 100fps), since frametimes are unchanged even with higher framerates (e.g. 200fps with 1/100sec frametimes) with the frames often being presented in an interleaved manner.

There are other SLI lag overheads especially when they are forced to do improved framepacing one after the other (for smoother motion), then if you disable the framepacing (increased stutter) the lag can go down. There is a certain amount of framepacing needed to make sure that the cards are in sync with each other, and that framepacing can add a few milliseconds input lag, depending on how the settings are configured.

AFAIK, the 1 & 2 approaches is probably identical, as is 4. Give them a try and see how it interacts with the game. For some games, competitive is better with SLI, and for other games, competitive is better without SLI.

The extra framerate can sometimes more than compensate for a sub-frame input lag -- but can be game dependent -- and settings-dependent.

The lag increase can be smaller than the difference between two different gaming monitors, but your mileage may vary.

I'll let others chime in with SLI experiences.
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Re: SLI input lag questions

Postby Sparky » 10 Jun 2018, 19:55

I believe most SLI implementations have more lag than a single card at the same graphics settings, though the variance may be lower.

The few games that use split frame rendering might have less lag than single card, but SFR doesn't scale as well in terms of framerate, so you don't see it as often.

If all you care about is competitive advantage, a single high end graphics card at low graphics settings is nearly always going to be the best option. It also shouldn't matter how you disable the second card, though I'm not aware of any testing on that question.
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