eGPU Performance: Internal vs. External Display

eGPU Resources, External Graphics Card 19 Comments

 

Now that an eGPU can accelerate a Mac’s internal display, the question that naturally arises is how significantly the performance of the eGPU would be affected. I wanted to not only provide insight on this question but also show the performance of a graphics card inside a Mac desktop, the Mac Pro tower. This is the last modern Mac with full-length, internal PCIe slots.

Performance differences between PCIe slot vs. External Display eGPU vs. Internal Display eGPU

The chosen graphics card for this comparison is an EVGA GTX 980 Ti Hybrid. It makes for a very nice pairing with the AKiTiO Node for an eGPU setup. The GTX 980 Ti Hybrid mounts inside the Mac Pro tower well with the only challenge coming from routing the liquid cooling lines.

The Mac Pro tower I tested is a 2010 model 5,1 with two 4x and two 16x PCIe 2.0 slots. In my opinion this is still the best Mac desktop available even though it’s six years old. The modular design makes upgrading components a joy. I’ve previously upgraded one of these Mac Pro towers to have 2x hex-core Xeon CPUs, GTX 980 Ti GPU, 128GB RAM, 512GB PCIe flash storage, and 4x 8TB Helium hard drives; all were mounted internally.

On the eGPU side, I’m testing the GTX 980 Ti Hybrid + AKiTiO Node with a Late 2016 13″ MacBook Pro through Thunderbolt 3 connection. For internal display acceleration, I’m using a headless ghost HDMI adapter. External display eGPU tests are through an HP 22″ monitor. The Unigine benchmarks ran at 1920 x 1080 fullscreen, max settings.

GTX 980 Ti HybridMax PCIe SpeedUnigine ValleyUnigine Heaven
Mac Pro Internal PCIe Slot32Gbps-PCIe2,026 (48.4 FPS)1,658 (65.8 FPS)
MacBook Pro External Display32Gbps-TB32,389 (57.1 FPS)1,756 (69.7 FPS)
MacBook Pro Internal Display32Gbps-TB31,814 (43.4 FPS)1,084 (43.0 FPS)

I’m sure you’re asking why the numbers from the Mac Pro internal 16x PCIe 2.0 slot are lower than External Display eGPU. Well, Apple crippled non-Mac GPUs to only be able to run at 2.5 Gbps lane speed. This gimpy connection effectively makes the graphics card run at 16x PCIe 1.1, which is close to 4x PCIe 3.0.

The important takeaway is the performance loss when you use an eGPU without an external display. Using an eGPU setup with an external display in macOS yields at least 30% higher performance than feeding that signal back into the internal display of your Mac.

It’s a considerable hit on performance. We all expected it though. Whether this trade-off is worth it depends on your situation and how you plan on using an eGPU. If you have questions about your external graphics card build, visit our forums.

 

[Nando] Q: How much bandwidth overhead does Optimus/X-connect accelerated internal LCD mode add?

Nando4 2019 update >> internal LCD mode is device-to-host traffic (incoming). Gaming and apps strain the host-to-device (outgoing) traffic. So feasible table results below are OK. Ignore the other waffle comparing bandwidths below since that isn’t applicable here.


As discussed on the eGPU.io forum
, subtracting this value from our total link bandwidth, with a reference of how much bandwidth is needed for acceptable performance will then tell us if our eGPU is truly a portable desktop-replacement solution. One that doesn’t require an external LCD.

 
Techpowerup have done a broad gaming test on different bandwidths, showing us you want a x4 2.0 16Gbps link to give real desktop replacement GPU performance (> 85%). That gives us a desirable reference point.
 
Below are the bandwidth requirements to send uncompressed data to the internal LCD @ 60Hz calculated using Kramer’s Bandwidth calculatorNVidia Inspector ‘Frame Rate Limiter V2’ software can lock this in to be doubly sure we do no exceed 60Hz, as any more is redundant due to that being the LCD’s refresh rate. Otherwise some games still report > 60FPS when benchmarked.
 
Do note * this does not take into consideration other tricks NVidia/AMD drivers may use to decrease internal LCD PCIe link traffic. So this overhead can be considered the worst-case scenario.
 
Resolution Internal LCD overhead* (Gbps) Theoretic remaining bandwidth for eGPU (Gbps)
32Gbps-TB3 16Gbps-TB2 10Gbps-TB1 4Gbps-EC2/mPCIe2
3840×2160 – 4k/UHD 14.9 17.1 1.1 unfeasible unfeasible
2880×1800 – 15″ Retina 9.3 22.7 6.7 0.7 unfeasible
2560×1600 – 13″ Retina 7.4 24.6 8.6 2.6 unfeasible
1920×1080 – FHD 3.7 28.3 12.3 6.3 0.3
1680×1050 – WSXGA+ 3.2 28.8 12.8 6.8 0.8
1366×768 – WXGA 1.9 30.1 14.1 8.1 2.1
 
 Blue : ~ 85% desktop GPU performance (x4 2.0 16Gbps or more bandwidth)

Lime: ~ 71% desktop GPU performance (x4 1.1 8Gbps or more bandwidth)

From this table comparison we see:

  • x4 3.0 32Gbps-TB3 NVidia/AMD accelerated internal LCD traffic traffic overhead still leaves us with at least our desired x4 2.0 16Gbps or more bandwidth for pure GPU traffic.
  • 16Gbps-TB2 with an external LCD to maximise it’s narrower PCIe link also gives ~85% desktop GPU performance levels. Internal LCD mode up to FHD can still deliver more than 71% desktop GPU performance.
  • Slower 10Gbps-TB1, 4Gbps-EC2, 4Gbps-mPCIe2 links will see compromised performance, particularly at higher resolutions. Those require an external LCD attached, application of Frame Limiting tweaks and disabling of eGPU audio devices to maximise their narrow bandwidth for GPU traffic.

 

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enjoy
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You can add my results too with fake display: 15′ MacBook Pro (Retina, Mid 2012, Thunderbolt 1) / Windows 10 / EVGA GeForce GTX 1060 SC 6GB / AKitio Thunder 2 External Display – 1376 (54.60 FPS) – Internal Display – 759 (30.1 FPS) – Internal Display – 1680×1050 (my Gaming resolution) – 1001 (39.7 FPS) – Here are another results from my friend without fake display (the laptop is with Intel Iris 6100 only): 13′ MacBook Pro (Retina, Early 2015) / Windows 10 / EVGA GeForce GTX 1060 SC 6GB / AKitio Thunder 2 External Display – 1246 (49.4… Read more »

enjoy
Member

Yes its at least 30% performance drop when we use the Internal Retina Display, but its better to use it because you have very good looking setup, without monitors etc on your desk!

If everyone is interested – to play all new and old heavy games on Very High/Ultra settings with 30-40 FPS right now you need around 1000 score on Unigine Heaven Benchmark. To play with 60 FPS You need at least 1200-1300 score and more!

Mike
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Mike

Can we get the corresponding benchmark scores on win 10 to elucidate the driver difference?

Anchoricex
Member

Hi THEITSAGE, Putting these together have been great. I have a 2016 15″ on the way, as well as a Node and a GTX Titan X. I’ve had one lingering question that I haven’t gotten an answer to anywhere that might be of use for the kind of content you like to throw on the front page if it can be figured out: Clamshell mode. Many people use their Macbooks in Bookend docks or hengedock vertical docks in clamshell mode with an external monitor. Is there a way to run the eGPU in clamshell mode? I understand that you’ll probably… Read more »

YangZA
Member

Have any of you played with Thunderbolt based video capture devices to loop the output of the eGPU back in via a second port? This way we can overcome the 30% loss by having the game render to HDMI rather than a fake display. See below:
https://www.blackmagicdesign.com/sa/products/ultrastudiothunderbolt

I do acknowledge that the price is rather prohibitive, but it does overcome some of the biggest issues with portable gaming.

Na Young
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Na Young

Hi Enjoy,

Do you know if I need to buy headless ghost if I use Windows via bootcamp ?
Will the performance of internal monitor be better with headless ghost/fake display ?

enjoy
Member

@NaYoung – No, the result will be the same!

Peter
Guest
Peter

Hi,

My laptop is Macbook pro late 2013 intel core I7-4850HQ 16GB ram.
What will be the best graphic card to get with Thunderbolt 2 box – Bootcamp setup?

imrazor
Member

So…does this performance penalty for using the internal display affect older, low-end cards that use less significantly less bandwidth? Say, for example a GTX 650?

nando4
Admin

Yes, there is performance penalty whenever using the accelerated internal LCD mode since display traffic needs to be routed back across the eGPU link.

Brandon
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Brandon

As Pascal-based GPUs are fairly new to the whole eGPU scene do you think we’ll get improved performance over the next several months?

David Backeus
Guest
David Backeus

Didn’t fully understand the 30% measured loss compared to the chart which seems to suggest that we should be at 85% of full speed (ie. around 15% performance loss).

Where is that extra 15% loss happening? Or did I misunderstand the chart?

David Backeus
Guest
David Backeus

Also would the 30% performance loss from outputting to the internal LCD be reduced by running games at lower resolution?

tbs43
Guest
tbs43

How much do the amount of internal RAM effect the performance on a system with a eGPU ? Im getting a Mac mini and dont wanna put too many RAM in the machine when I plan to get a eGPU TB3.