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