iGPU *and* eGPU - can the system use both?

[vocalnick]

Hey all,

The basic question is in the header - if I'm running a 16" with an iGPU, but there's also an eGPU driving the display, is the iGPU still available to the system for speeding up things like video rendering?

More Detail:

I have a new 16" arriving any day now. The ARM transition sent me into a bit of a tailspin, but I really need a new machine, and I still have a few mission critical Windows applications, so I think it's the right choice for now. But I'm a bit worried about the external monitor heat/fan noise situation, as I use my machines docked quite a bit. I don't currently have any TB3 gear (my existing system is based around TB2) so I'll have to buy a new dock to get multi-monitors.

To sidestep the ext display noise/heat issue, I'm thinking of skipping the premium hub and going for a lower end eGPU to drive my displays (and power the laptop while docked), and then a just a basic dongle to expand the I/O a little, which I'll also use on the road.

So far so good (I think?) but I've noticed that eGPUs tend to take a performance hit when being used for rendering power when compared to a dedicated internal GPU - something to do with the limited bandwidth of the TB3 cable vs having the CPU and the iGPU side by side.

So my question (finally!) is can/will MacOS use an iGPU to accelerate these tasks if one is present, even if there's an eGPU driving the displays? Or does plugging in the eGPU just simply disable the internal unit?

 

[casperes1996]

Technically, yes, but most apps wouldn't use both. But technically the programming interface available does allow it. A lot of the time the AMD GPU in a 16" will outperform an eGPU, especially with the higher end 16" options; See Max Tech/Max Yuriev on YouTube for numbers.

 

[vocalnick]

A lot of the time the AMD GPU in a 16" will outperform an eGPU, especially with the higher end 16" options; See Max Tech/Max Yuriev on YouTube for numbers.

Yeah, that's my concern. eGPU solves the heat/noisy fan problem on the 16" with an external monitor, but I'd prefer not to take a performance hit if possible...

 

[casperes1996]

Yeah, that's my concern. eGPU solves the heat/noisy fan problem on the 16" with an external monitor, but I'd prefer not to take a performance hit if possible...

Another solution I guess is having long cables, putting the Mac far away and putting a desk fan under it, having it sit on a platform... But I mean heat should stay within spec regardless

But if you’re at the point where you’re ready to spend the money for an eGPU, aren’t you also almost at the point where you could have both the laptop and a desktop Mac? Might solve it too.

But I have no ideal solution. There’s no way for the system to know in advance which chip would perform a certain operation faster. Apps can ask for a specific GPU when several are seen, but most will jus ask for either a high performance or low power chip and not specify further than that

 

[vocalnick]

But if you’re at the point where you’re ready to spend the money for an eGPU, aren’t you also almost at the point where you could have both the laptop and a desktop Mac? Might solve it too.

That's what I'm doing now (O.G. 2012 rMBP & a 6-core trashcan) but I waste a lot of time keeping them synced with applications and plugins, and still occasionally run into trouble on that front. I'm really keen to keep everything in the one unit.

But yeah, if you can find me a desktop Mac that matches the performance of the i9 8-core for the price of a low-tier eGPU I'll definitely take a look at it

But I have no ideal solution. There’s no way for the system to know in advance which chip would perform a certain operation faster. Apps can ask for a specific GPU when several are seen, but most will jus ask for either a high performance or low power chip and not specify further than that

Yeah - that make sense. Thanks