Better performance with Iris Pro graphics than 750m? (rMBP 15")

Discussion in 'MacBook Pro' started by anthonya1999, Aug 22, 2014.

  1. anthonya1999 macrumors member

    anthonya1999

    Joined:
    Aug 22, 2014
    #1
    I just bought a retina macbook pro, and I got the model with the 750m graphics card. When I turned off the option that said automatic graphics switching in the energy saver section of system preferences, it gave me a message that said the computer would always use high performance graphics. However, I noticed some lag when I started using it, especially with animations. I went to the apple store, and told them the problem. They said that this was because since the NVIDIA graphics card has 2GB of memory, that acted as my RAM, and the 16GB was not actually doing anything/being used, and with the switch turned on, it actually uses BOTH GPU's (or at least they work together somehow). So he told me to turn the switch back on.

    I feel like since the computer told me that it would be "high performance", the guy at the store was contradicting what the computer was telling me...does this make sense? Was the guy at the apple store telling me to turn it back on because that's the default or something?

    Thanks.
     
  2. remingtonjd macrumors newbie

    Joined:
    May 11, 2012
    #2
    Interesting... I have heard of these issues and did not investigate until my rMBP arrived today! (Proud owner!!). I would like to know the answer to this as well as I frequently game on my Macs and was hoping to take advantage of my brand new 750M.
     
  3. blooperz macrumors 6502

    Joined:
    Dec 10, 2013
    #3
    sounds pretty wrong to me...I'm no expert but that sounds like a load of **** from someone that didn't have a real explanation....I'd get a 2nd opinion if I were you...
     
  4. Tea-Aholic macrumors 6502

    Joined:
    Dec 8, 2011
    Location:
    Melbourne, Australia
    #4
    The guy is talking complete nonsense.

    The 16GB of RAM is always available to the system.

    With "Automatic graphics switching", the Intel Iris Pro will be utilised normally with the GT 750M coming on automatically when programs require more GPU power.

    With it unchecked, only the higher performance 750M will be used.

    The GPUs are never working at the same time, either one or the other.
     
  5. FuNGi macrumors 65816

    FuNGi

    Joined:
    Feb 26, 2010
    Location:
    California
    #5
    Some applications do use both GPU's but they have to be coded to so (FinalCutPro, Adobe Premier Pro) but that does not appear to be what was causing the issues the OP was having. The Apple Genius was making up a story on the spot. OP, download gfxCardStatus and you'll see which applications trigger the NVIDIA card – not all do and you'll be able to more passively assess if you have a glitchy system or it was just a one-off event. I've had no issues related to whether I'm using the iGPU or the NVIDIA GPU on my late 2013 rMBP.
     
  6. Celedral macrumors 6502

    Celedral

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    May 29, 2008
    Location:
    Los Angeles
    #6
    Wow, these specialist are getting more and more incompetent. They can say anything and people will believe them since they wear an apple logo. I remember once a specialist was telling a customer all the laptops were QUADCORE when clearly they were dual core i7 (no QC at that time). I was furious, but didn't want to butt in at that time.
     
  7. merrickdrfc macrumors 6502

    Joined:
    Jan 8, 2011
    Location:
    Manchester
    #7
    Not sure what the OP is experiencing, I have zero UI/system lag running either the 750M or Iris Pro GPU - Mid 2014 MBP.

    But yeah you can't really trust what they come out with a lot of the time, I remember over hearing a conversation from a specialist informing someone that the 'MacBook Air can be so fast due to the fact it doesn't need a processor, it's a completely new system architecture' - back in 2010, not sure the guy would have cared either way but still not really very professional.
     
  8. Tea-Aholic macrumors 6502

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    #8
    There is NO application that uses both GPUs. Final Cut only uses the discrete card.
     
  9. FuNGi macrumors 65816

    FuNGi

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    Feb 26, 2010
    Location:
    California
    #9
    I guess I was operating under old information regarding openCL providing the ability to say, use both the old 9400 and 9600 graphics chips in older macs. What I said appears only to pertain to the dual GPU's in mac pros. Apparently, the Intel GPU in the rMBP is deactivated once the GPU kicks in. I'm curious if the new iMacs contain CPU's with our without a iGPU?
     
  10. leman macrumors 604

    Joined:
    Oct 14, 2008
    #10
    OS X allows any number of available GPUs to be utilised at the same time, no matter which GPU is currently used to drive the display. There are APIs to do that. Your application will need to request it explicitly though.
     
  11. Tea-Aholic macrumors 6502

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    Dec 8, 2011
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    Melbourne, Australia
    #11
    The entry level iMacs don't have discreet graphics so they just onboard Intel Graphics. The upper end ones have discrete NVIDIA graphics. There is no GPU switching on iMacs, even with the discrete configurations because there is no power constrains like on notebook computers.

    Please stop thinking that the MacBook Pro can use both GPUs at the same time. OS X being able to do so doesn't mean the MBP can. Apple engineered to have either Integrated or Discrete at a single time, not both.
     
  12. leman, Aug 27, 2014
    Last edited: Aug 27, 2014

    leman macrumors 604

    Joined:
    Oct 14, 2008
    #12
    Sorry, but you have no idea what you are talking about. I have actually written applications which use both GPUs at the same time. Works like a charm.

    You are confusing the notion of the 'online' GPU (the one that is currently used to drive a display) and that of 'used' GPU (the one your application uses for this or other purpose). You can still use a offline GPU to draw to memory buffers and than copy that buffer to your online GPU.

    Please refer to Apple developer documentation for more information.

    P.S. I can also point you to this thread, where this is discussed in more details (with a demo): http://forums.macrumors.com/showthread.php?t=1688619
     
  13. Tea-Aholic macrumors 6502

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    #13
    As much as your experiment went, I don't see that the current setup can be worthy. There are no applications that do this, reason being it is impractical due to the setup.
     
  14. TechZeke macrumors 68020

    TechZeke

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    Jul 29, 2012
    Location:
    Rialto, CA
    #14
    This thread is as confusing as the Genius at the Apple store telling the OP that his system wasn't using system RAM because the dGPU was enabled.
     
  15. Cibike macrumors member

    Cibike

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    Nov 10, 2013
    Location:
    EU
    #15
    I believe that OS X basic animation are designed for intel integrated graphics since every mac has this graphics and dGPU is reserved just for apps with great demand on GPU
     
  16. leman macrumors 604

    Joined:
    Oct 14, 2008
    #16
    So now that you have been proven wrong, you try to substitute the topic :rolleyes: To refresh your memory, we were talking about whether its possible, not whether its worthy.

    That aside, I agree that the usefulness of such setup is questionable in most cases. There is an overhead in synchronising the GPUs, so there are only few situation which I can envision, that would benefit from this technique. One notable exception are multi-GPU computers like the Mac Pro, where the potential gain is higher than the overhead. E.g., one could easily program an Alternate Frame Renderer using this technique.
     
  17. Tea-Aholic macrumors 6502

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    Dec 8, 2011
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    Melbourne, Australia
    #17
    Well, practicality is important, so if it's not really practical to do then why bother. If you could use both GPUs at the same time to boost performance significantly Apple would have done that.

    The Mac Pros 2X GPU setup is designed to be high performance, the ones on the notebooks aren't. Even my Sony VAIO had 2 GPUs but aren't able to use both at the same time.
     
  18. SarcasticJoe macrumors 6502a

    SarcasticJoe

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    Nov 5, 2013
    Location:
    Finland
    #18
    That really doesn't sound right... Partly because the 750M is about twice as fast as the Iris Pro and partly because the Iris Pro is limited to a maximum 1,5GB chunk of the system RAM. Not only does the 750M have more RAM (2GB as previously mentioned), it has faster RAM of a type called GDDR5.

    The real reason here is probably that you're using software that hasn't been tested on the 750M and thus relies purely on the CPU to avoid any unexpected problems. The new Mac Pro had a similar problem with Adobe Premiere where it actually ran slower than on some higher end old machines because on the old machines it utilized the GPU and on the new machines it ran purely on the CPU.

    You really shouldn't go to retail to ask anything but basic stuff because they're pretty much clueless when it comes to anything slightly more technical. They don't teach them any of the more technical stuff, they're there to sell computers to old ladies and other semi-clueless people who can't look up the facts on their own.
     
  19. MagicBoy macrumors 68040

    MagicBoy

    Joined:
    May 28, 2006
    Location:
    Manchester, UK
    #19
    The rMBP can utilise both GPUs simultaneously for OpenCL, but not as a video display device.

    Don't believe me? Try the Luxmark benchmark app.
     
  20. leman macrumors 604

    Joined:
    Oct 14, 2008
    #20
    I gave a link above to where I showcase a program that uses both the iGPU and the dGPU for rendering to different portions of a window at the same time. Yes, it is not of much practical importance, but it is possible.
     

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