Tests Show Limiting Frame Rate Dramatically Improves Laptop Battery Life

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.

Via:  Hot Hardware
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