talbotini

Q: Mac Pro multiple graphics card performance

I have a 2008 Mac Pro 3,1. It is the 2x Quad Core Xeon 3.0 ghz model. It came with a Radeon 2600 XT 256MB graphics card. When I got it I added a Radeon HD 5770 1GB card. It works great but I have run into a strange performance issue and I am trying to wrap my head around it.

 

I have two identical 1080p 24" monitors. Typically one is plugged into the 2600XT and the other into the HD 5770, and I will use one for running graphic heavy software like the Adobe Creative Suite and games, and the other for mundane tasks like web browsing and monitoring voice chat software.

 

When I play video games on it I monitor the frame rate while I run them. I have found that while I am running the second monitor my frame rate drops in game. But if I completely remove the 2600 graphics card and run one monitor I get similar frame rates that I would with one monitor if I leave it in. I would think that running the second monitor on a separate graphics card would have no effect on the performance of the primary display, but that doesn't seem to be the case.

 

I suspected the CPU might be the culprit, even though I highly doubted this would be the case considering the processor I am running, but I downloaded some additional performance monitoring software and the CPU or the RAM (16GB) is never anywhere close to maxing out. From what I can tell both monitors are borrowing from the GPUs somehow, but running one monitor with one GPU is giving me better frame rate than two monitors with two GPUs. Even while the one monitor is doing almost nothing at all. Theoretically I should have enough GPU power to easily run 6 monitors, so I am perplexed by this drop in performance with just two on separate GPUs.

 

Is there a way to isolate the graphics cards each to their own monitor, so that I can expect the performance I am getting out of a single card while running dual monitors (or more) with two cards?

Mac Pro, OS X El Capitan (10.11.6), 3,1 3.0Ghz 2x Quad Core Xeon

Posted on Aug 11, 2016 9:06 AM

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Q: Mac Pro multiple graphics card performance

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  • by Johnb-one,

    Johnb-one Johnb-one Aug 11, 2016 11:39 AM in response to talbotini
    Level 4 (1,879 points)
    Desktops
    Aug 11, 2016 11:39 AM in response to talbotini

    that's an interesting question....no, you can't isolate the graphics cards, each to their own monitor, and you can forget about linking them together (aka CrossFire)...it might also depend on what slot each graphics card was in...one has x16 lane width and the 2nd not so much (don't quote me on the exact specs, though), If you wanted better performance, I suppose you could get a beefier video card to replace the X2600, maybe a 5770? Also,. the X2600's are known for being dust collectors. Maybe give it a good blast after your Mac has been shut down, you took off the side panel and touched the metal frame, failing that, there might be a few more PC graphics cards that could be supported in El Capitan then when the X2600 was released. I can't speak for how well they work right out of the box, or which ones exactly are supported, but there must be some of them. you could try looking at xlr8yourmac.com for a rough guide. Apple isn't exactly forthcoming about which ones will and won't work....we have to go by others' experiences...

    good luck to you

    John B

  • by Grant Bennet-Alder,

    Grant Bennet-Alder Grant Bennet-Alder Aug 12, 2016 9:36 AM in response to talbotini
    Level 9 (60,692 points)
    Desktops
    Aug 12, 2016 9:36 AM in response to talbotini

    Any ONE graphics card you can plug into your Mac Pro has the ability to drive multiple displays without slowing down, because driving and refreshing displays is largely done with Hardware.

     

    The hope that adding a second display CARD (with displays attached) somehow boosts performance is a false hope.

     

    All other cases mean you are creating an Extended Desktop that spans two cards. This will by definition be slower, as the CPU will need to cut up the picture into several pieces for each graphics card, then assign rendering of its section to each card. Some rendering of areas near the card boundaries will need to be done twice, then clipped.

     

    Only an organization like the late 2013 Mac Pro, with its second graphics processor dedicated to ONLY GPU computing, can expect any speed improvement from adding a second graphics card.