Graphics smoother with two displays than with one?

[ProMod]

Take a look at my signature for my machine's specs.

I'm noticing something I find to be counterintuitive. When running my MBP in clamshell mode with my 23" ACD connected, overall graphics performance is sharply reduced. The dock animation is choppy, windows opening and closing are choppy, opening stacks from the dock is choppy, etc. This is when running one display only, the external ACD.

When I run my setup as dual display, using both the built-in MBP display and the external (non-mirrored), graphics performance returns to normal and is silky smooth.

This seems strange to me because by doubling the load on the GPU, I get much better performance. I see no difference in either scenario by toggling "automatic graphics switching" on or off.

Does anyone else experience this same thing, or have an explanation or solution? I use the dual display setup more times than not, but I'm curious why performance drops off so dramatically simply by closing the lid of the MBP and using only the external display.

 

[iThinkergoiMac]

The only explanation I can think of is that, in clamshell mode, it's still defaulting to the integrated GPU, but extended mode forces the discrete GPU. You said you've tried turning on and off the automatic switching... does that mean you've tried forcing the discrete GPU?

 

[ProMod]

You said you've tried turning on and off the automatic switching... does that mean you've tried forcing the discrete GPU?

If toggling that setting to "off" forces the discrete GPU, then yes. I'm not aware of any other method to explicitly force the discrete GPU. I'm not big into installing third-party apps to control the GPU, fans, etc.

I see what you're saying though. Somehow by running in clamshell mode, even with the auto graphics switching set to "off", maybe it still runs on the integrated graphics because it's only pushing one display. Though by that theory, you would think the performance would be degraded when using only the built-in display, and that's not the case. Simply put, everything is smooth when using only the notebook display, or both the notebook and the external. Everything is choppy when using only the external.

 

[iThinkergoiMac]

If toggling that setting to "off" forces the discrete GPU, then yes. I'm not aware of any other method to explicitly force the discrete GPU. I'm not big into installing third-party apps to control the GPU, fans, etc.

Try gfxcardstatus. I've heard great things and, if nothing else, it will give you a way to nail down which GPU is being used.

 

[ProMod]

Try gfxcardstatus. I've heard great things and, if nothing else, it will give you a way to nail down which GPU is being used.

I installed gfxcardstatus. It works very well. I've been able to determine that the discrete card is in use at all times when an external display is connected. That makes it even more confusing why there is a decrease in performance when using one display rather than two.

On a positive note, I've set up gfxcardstatus to force the system to use the integrated card only while on battery, and have noticed quite an improvement in battery life.