Tests Show Limiting Frame Rate Dramatically Improves Laptop Battery Life

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News Posted: Mon, Mar 31 2014 1:12 PM
When Nvidia unveiled its new GeForce 800M mobile family a few weeks ago, it talked about a new set of improvements and innovations coming to laptops with through the GeForce Experience program. In the future, applications would have the option to dramatically improve battery life by limiting in-game frame rates as well. Nvidia claims that its upcoming profiles will do more than simply limit a game's frame rate, but it identified that option as one of the most useful ways to squeeze better battery life out of a system while gaming.

We decided to test the idea and see just how much of a difference it could make. In this case we used an Alienware 17 laptop equipped with an AMD GPU  (the R9 M290X) instead of an Nvidia GPU, but since we're testing one idea rather than the entire GeForce Experience update, we should still get some useful data on what kind of improvements a gamer might see from running a frame rate limiter on a GPU.

Our game of choice?  Diablo III: Reaper of Souls. D3 offers the option to set a specific Foreground FPS target, which simplifies the testing process (We'll cover how to enable FPS limits for other games a little later on).



We set this to 30 FPS, enabled V-Sync, and ran through a 30 minute play session, with the laptop attached to a Kill-A-watt meter to record total power consumption over that time. We then repeated the test, only with V-Sync disabled and the "Max Foreground FPS" set to the default of 150 fps. The results were quite interesting:


Running the game at a constant 30fps reduced the total power consumption by nearly a third, from 158W average to 107W average. It also reduced the heat -- I was gaming with the laptop actually on my lap and the system was noticeably cooler. We didn't formally measure temperatures in this test, but the impact on both thermals and battery life will be commensurate.

We ran a third test at 1280x720 with all detail levels reduced to minimum, but saw no further improvement. Nvidia noted in their announcement that the battery life gains it can deliver will be different from title to title; evidently Diablo 3 isn't a game that sees much boost from normal detail level adjustments. Whether Nvidia can modify this further through deep driver settings is something we won't be able to test for awhile yet.

As for the actual experience of playing at 30Hz, I'll admit, it's not the greatest -- but it's something you can get used to. If you're trying to squeeze a bit more battery life out of a system, the tradeoff seems to be a worthwhile one.

Saving Battery Life In Other Games

Gamers without a GeForce 800M won't see the full spectrum of Nvidia's improvements, but AMD and Nvidia users can both benefit from frame rate limitations right now. Nvidia users will want to use Nvidia Inspector, while AMD users will once again be using Radeon Pro. From NvInspector, users should scroll to the "Common" subhead, then select "Frame Rate Limiter" as shown below.



This will allow you to set a frame rate target for either all games or for specific titles.

AMD users can accomplish the same thing using Radeon Pro. Once you've installed the app and selected either Global or a specific game profile, you can choose to either limit the game to no more than 30 fps, or you can enable double V-Sync (an effective 30Hz refresh rate on the vast majority of monitors), then lock the frame rate to the refresh rate.



You can also specify a target refresh rate or a steady FPS speed -- if you want, say, 45 fps.

This is less likely to be an issue with Intel HD Graphics, which often struggles to reach higher frame rates in any case, but it may be possible to do the same trick on an Intel system by defining custom refresh rates and resolutions using Intel's desktop tools. Games that take their resolution and refresh settings from Windows should pick up this information.

The boost isn't large -- you won't double your battery life in Diablo 3 from this kind of tweak -- but if you're trying to squeeze out an extra 20-30 minutes of game time during a long flight, this kind of change should get you there.
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Jason replied on Mon, Mar 31 2014 1:27 PM

Really good tip to help get a little more time out your battery to game. although I would rather have my FPS around 60, even if the difference between 45 and 60 to the human eye is minimal. But my friend uses a laptop to game on trips so I gotta show him this

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Yep its a Great Tip got to let me gaming dudes know

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This seems like it should be fairly elementary. If the GPU doesn't work as hard, it should consume less power.

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Joel H replied on Mon, Mar 31 2014 1:57 PM

Sure, but how much less? That was the question.

Without any frame limiting at all, the game ran at about 75 fps at the settings I was using -- so cutting the frame rate by 60% cut the power consumption by 33%. What's more interesting is that in this title, turning all detail levels down *and* clamping the frame rate did nothing to help the power consumption situation.

In other words, even though the GPU was working "less hard" (1280x720, minimum detail) it still drew the same amount of power at 30 fps in both test cases. That's not necessarily what I would've predicted.

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You would be surprised on how many people wouldn't even know what a frame rate is.

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Joel H replied on Mon, Mar 31 2014 2:13 PM

Sean,

I really wouldn't.

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sweet thanks. i wonder thats why my old battery dies in a mater of minutes

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amd did this some time ago

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BobBoby replied on Mon, Mar 31 2014 5:03 PM

Lol well if the GPU doesnt have to work as hard to increase fps...battery life would obviously be longer

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I love how everytime AMD does something, other big names make it a big deal and steal credit.

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I do not get way everyone is always so excited about getting more than 60 fps anyway. Most monitors do not refresh at over 60 fps. Also, the human eye cannot tell the difference at more than 20 fps. So running a computer too hot and using unneeded resources to pull 120 fps is just a waste. Personally, I limit all my computer to 40-50 fps. This allows for little network dips that will make it go down to 30 fps without me ever noticing, and leaves the rest of the computer resources to process game info improving performance.

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Hmm... That's an interesting perspective ShawnLauseng. Given the fact that it's well known at least 95FPS is needed for optimal immersion for VR (http://en.wikipedia.org/wiki/Immersion_(virtual_reality)), there is some value of going over 20-60 FPS.

There's a reason why a lot of console and gamers are adamant their games play at least 60FPS instead of just 30FPS. You CAN tell the difference, unless you meant you can't tell the difference of the same footage being sampled at 2 different framefrates unless the difference between the two samples is greater than 20FPS.

At the end of the day, the variance can be too severe, making the pursuit of higher frame rates pointless.

The problem with high frame rates variance is the fact GPUs often render frames as quick as possible while Monitors simply render frames at a fixed rate. This leads to an asynchronous refresh cycle that leads to things like screen tearing. For that reason, sometimes, people just try to fix their rate to their monitors.

The problem that occurs with that is the fact you can have choppy visuals/stuttering if your GPU has to repeat frames continuously while waiting for your monitor's refresh cycle that's fixed.

The gamebreaking solution to both these problems is Nvidia's Gsync technology that'll force the MONITOR to wait for the GPU to present a new frame for perfect synchronous behavior between the two.

No screen tearing, no stuttering--a game-changing experience. ATI is looking into a alternative (it's going to be called FreeSync supposedly). In the meantime, with these monitors coming out this year, Nvidia's GPUs are a no-brainer to get these days--if it wasn't obvious enough with their 82% workstation marketshare, their outstanding propriety tech like CUDA, ShadowPlay, and PhysX; and so on...

That in mind, I would think the battery life variance would be minimal (thus the amount of time before the battery dies is more predictable) with Gsync on for a test like this, but it'd be interesting its effect on battery life...

Can Joel Hruska look into this?

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Joel H replied on Wed, Apr 2 2014 4:12 PM

I cannot test G-Sync but can confirm the human eye can perceive well above 20 FPS.

http://www.cameratechnica.com/2011/11/21/what-is-the-highest-frame-rate-the-human-eye-can-perceive/

The human eye does not perform full refreshes and does not see in frame rate terms, so any attempt to quantify the speed of the eye in these terms is extremely difficult. Nonetheless, there's no question we see above 60 fps.

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Hi Joel, great article!

We've been aware of this for some time now - and we have developed a tool which can bring you benefits from both worlds - save power AND keep the gameplay performance. In essence it is a "smart" framerate limiter - it limits the framerate selectively, and gives you full power when needed.

It's free - you can get it here: http://www.hialgo.com/TechnologyCHILL.html

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Thanks for the follow-up Joel, and the resource about the extent the human eye can see frames...

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