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Short answer TL:DR
Disclaimer: I’m not up to date on eGPUs or the new Thunderbolt 4, but here’s what I know.
SPEED/PERFORMANCE:
eGPU’s are slower than desktop GPUs,
but the answer might be more complicated than that and beyond my knowledge (explained in the more detailed answer below)
I’ve read that you can expect about a 20% performance drop if your eGPU is hooked up to an external monitor. (Not sure how much Blender is affected).
It’s even worse on laptop screen: Up to 50%. I’m guessing that carrying an external colour-accurate monitor around was not what you had in mind But that’s from a 2017 post.
ANYONE KNOW ANYTHING ABOUT THUNDERBOLT 4?
TB4 (Thunderbolt 4) is new. TB3 is what most eGPUs are right now afaik. Maybe you want to wait for TB4 Enclosures tho. I have no idea. Apparently it’s the same speed???
CHOOSING A LAPTOP:
Be careful when choosing an ultrabook laptop! There’s different types of thunderbolt (TB1, TB2, TB3, and now TB4), and some thunderbolt are slower!
Also, eGPU performance may depend on how recent the CPU is and maybe other stuff too!
IS AN EGPU REALLY THAT CONVENIENT?
Also, modern eGPU might not be as plug-and-play-simple as you think and might require some troubleshooting.
So read up on https://egpu.io/best-egpu-buyers-guide/ and watch YouTube reviews to see what you’re getting into.
More Detailed Answer:
Knowing about PCIe speeds and Thunderbolt 4, 3, 2 and 1 speeds might help understand how much slower an eGPU is compared to a desktop.
(Also, I’m pretty sure laptop GPUs are slower than their desktop versions in general.
Here’s a helpful PCIe Speeds Chart
[https://www.deskdecode.com/wp-content/uploads/2020/02/PCIe-Version-difference.jpg]
BUT note that 1 GB/s (i.e. 1 GigaBYTE/s) does NOT equal 1 Gbps (i.e. 1 GigaBIT per second).
So use an online Gbps to GB/s converter
PCIe has two numbers. The "#.0 one and the “x##”. The higher both numbers are, the faster the PCIe.*
TB3 (Thunderbolt 3) and TB4 are the fastest afaik. (M.2 is, too, but I think that’s a DIY cut-a-hole-in-your-laptop’s-case kind of stuff you probably don’t want). *
**Apparently, TB4’s the same speed as TB3 afaik? Does anyone else know what advantage a TB4 eGPU enclosure would/will have??*
*RTX 3090 bus speed is PCIe 4.0 x16, *
[https://www.videocardbenchmark.net/gpu.php?gpu=GeForce+RTX+3090&id=4284]
- which is 31.5 GB/s, *
- which is the same as 252 Gbps. Much faster than eGPU’s 40 Gbps*
But most GPUs aren’t that fast. They only have a bus speed of PCIe 3.0 x16.
[https://www.videocardbenchmark.net/gpu.php?gpu=GeForce+RTX+2080&id=3989]
Which is 15.8 GB/s, or 126.4 Gbps. But that’s still much faster than TB3’s 40 Gbps.
But I recently learned that, for example, most AM4 desktop motherborad chipsets (from 2017 to 2020) don’t even have that full PCIe 3.0 x16 speed. The only one that has that speed is the high end X570 chipset (it’s actually the faster 4.0 PCIe 16x)
[https://en.wikipedia.org/wiki/Socket_AM4#Chipsets]
So have some people been using PCIe 3.0 16x GPUs at partial speed for a while? Or do most GPUs not reach that speed? I don’t know why, but i noticed that lots of GPUs have “Bus speed PCIe 3.0 16x” on videocarbenchmark.net.
Hopefully someone here who knows about GPUs in general can answer.
But yeah, eGPU looks cool and convenient. For a while, I really wanted one. But it’s extra cash for lower performance. Hopefully it’s as convenient as it seems, or will be in the future.