The dGPU: Killing Battery Life

The 15 and 17-inch MacBook Pros have a discrete GPU that only turns on if you fire up an application that really needs it—at least that's how it is supposed to work. In practice, the discrete GPU takes over control if your application uses any one of a number of frameworks—and some of the time, the dGPU simply isn't necessary.

Case in point, launching Chrome won't trigger a dGPU switch but the moment it encounters Flash the discrete GPU will take over. The bad news is that even if you close all Chrome windows, the dGPU won't power down until you quit chrome entirely. The same is true for Photoshop. Launch the application and you're still on the iGPU. Actually open up an image and the dGPU takes over. Even if you close all open images and just leave the Photoshop application open, the dGPU won't relinquish control. FaceTime and anything using the integrated camera also require the dGPU, despite it being totally unnecessary.

If you connect any external display to the 15 or 17-inch MacBook Pro that also forces the dGPU on, at which point both the integrated panel and external display are driven by the dGPU. There is no funny frame buffer copying going on, both the integrated and discrete GPUs have their own connection to the display.

Apple also fails to provide a way of turning off the dGPU by default—the best you can do is shut off the iGPU and just use the dGPU entirely. Thankfully Cody Krieger's gfxCardStatus tool gives us exactly what OS X does not. Version 2.0.1 adds support for the 2011 MacBook Pros.

I'm going on and on about the dGPU because it's state can seriously impact battery life. The numbers below should help put that in perspective for you:

Impact of Discrete GPU on Battery Life
15-inch 2011 MacBook Pro Light Web Browsing Flash Web Browsing
Integrated GPU (Intel HD 3000) 8.85 hours 7.03 hours
Discrete GPU (AMD Radeon HD 6750M) 5.67 hours 2.97 hours

Even just browsing the web, the dGPU being on drops battery life by 35—60%. Under full CPU load I suspect the percentage difference would be smaller, but still significant. The worst part of this all is that without gfxCardStatus you can negatively impact battery life by doing something completely innocent like accidentally leaving an application open. Given how much OS X is tailored to simply closing windows when you're done with them and not quitting applications, an overly aggressive dGPU can really be an issue.

Thankfully we do have gfxCardStatus but there's honestly no reason Apple shouldn't include this functionality with OS X from the start.

The GPU Comparison Display Quality
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  • Brian Klug - Friday, March 11, 2011 - link

    So I roll with my optical drive replaced with a Vertex 2 SSD inside an OptiBay daily. It's an awesome combination if you can do it.

    One problem I noticed however is that Apple's EFI won't boot optical drives other than their own $79 external drive. That means if you want to use boot camp, you have to install Windows with the optical drive (internal SATA) connected, then do the swap to OptiBay SSD + HDD.

    -Brian
    Reply
  • AmdInside - Thursday, March 10, 2011 - link

    I'm just not that interested in this years lineup. The better CPU performance is nice but given how much more features Windows notebooks provide today, I feel I can rely on Windows notebooks as a desktop replacement much more than I can a Macbook Pro. I will still use my MBP 13 2010 for home use but for business, I rely on my Windows laptop. Reply
  • Braddik - Thursday, March 10, 2011 - link

    Amazing article! I love how thorough and detailed you are. Mad props! I work in a medium-large size organization and the Dell vs. Apple debate is hot right now. Our Mac user base is growing, but the majority of the organization is Dell. I would love an article that compares the performance/value/support of MacBook Pros vs. Dell Latitudes in the Enterprise environment. Which is better? Can/should organizations feasible make the move to a full Mac environment? I would love your input! Thanks! Reply
  • Anand Lal Shimpi - Friday, March 11, 2011 - link

    Thanks for the kind words. I'm not sure I can offer much advice in terms of how the MBPs fare in an enterprise environment. While I know of many corporations that now issue OS X systems as an option, those systems typically have some form of Windows on them (either via Boot Camp or as a VM).

    Perhaps someone else may be able to offer more input?

    Take care,
    Anand
    Reply
  • Chloiber - Thursday, March 10, 2011 - link

    I still think it's too early to completely throw away desktops.
    With my T410, I also made the change to use it as my main "working" computer. At home, I can dock it and use my big, comfortable screen. It's very fast in "normal" usage like simple programming, texting, surfing, some "medium" load graphical stuff, some MATLAB etc. etc. - it's just perfect.

    But as soon as I want to do really heavy stuff like hours of video encoding, I still switch to my desktop with 4 or more cores and a fast dedicated GPU. It's just not the same and I really don't like to stress my laptop that much (allthough it is a Thinkpad). I don't know - I'm even less comfortable with a quad in my notebook. I don't know, but it's just not the same as a Desktop for really heavy stuff.

    I do like the new MacBooks - I don't like the resolution of the 13" model though...it's awful...
    Reply
  • Ushio01 - Thursday, March 10, 2011 - link

    While i expect a Mac Pro refresh late 2011 early 2012 I wonder if it could be the last. With the discontinuation of xserve and as this review demonstrates a mobile CPU matching less than year old server level parts in performance and thunderbolt allowing highspeed access to a NAS box I can see Apple discontinuing there last product targeting solely the professional market and truly becoming a CE company. Reply
  • rural_oregon - Friday, March 11, 2011 - link

    Yes, I have to agree with you. With macs only 20% of Apple's total revenue, and the mac pro only perhaps 5% of the mac revenue, at some point soon it just won't be worth the effort. I think it's even possible that there may not even be a sandy bridge mac pro. Reply
  • tipoo - Friday, March 11, 2011 - link

    It certainly seems like a possibility. Apples focus really has shifted to mobile devices, and its Mac revenues are only about a fifth of what the company makes. I can't imagine the Pro is any substantial percentage of their revenue, 1-5% perhaps. Might not be worth the effort for them. On the other hand, it would irk mac developers and creative pro's. Reply
  • wast3gat3 - Thursday, March 10, 2011 - link

    Just a short thanks for such an in-depth review.
    I have a mid-2010 15" MBP and am upgrading this week to the 2011 15" MBP as the performance gain is just too good to pass up. Interesting though that Apple locks the TRIM support in to their own SSD. I'm still going with the 7200rpm 500GB option and will move that disk to an opti-bay and the 3GB controller now knowing that they are using B3 stepping and fit a 6gb sata SSD. Hopefully LION will fix that TRIM support or some clever cookie works out how to enable it.
    Once again thanks!
    Reply
  • Kuril - Thursday, March 10, 2011 - link

    I always wait for AnandTech reviews because they are almost aways the most comprehensive. I love how the technology behind the reviewed product is summarized, and that there is some footwork to better describe the exact hardware being used (e.g., CPUs for MacBook Pros).

    Thanks for the informative reviews. No one comes close.
    Reply

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