Enclosures with Two Thunderbolt Controllers for I/O for Oculus Link VR
 
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Enclosures with Two Thunderbolt Controllers for I/O for Oculus Link VR  

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dancole42
(@dancole42)
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Joined: 3 months ago
 

I'd like to be able to connect an Oculus Quest via Link cable directly to an eGPU to avoid the loopback bottleneck. As far as I can tell, Link is just a USB-C cable. I've heard that certain enclosures have issues with their USB ports when on a shared controller. I've also read that the Razer Core Chroma addresses this issue by using two separate Thunderbolt controllers.

Is there a listing available somewhere of enclosures that have two TB controllers, aside from the Razer?

HP Spectre x360 13" FHD i7-1065G7


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joevt
(@joevt)
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Joined: 3 years ago
 

In the buyer's guide, any eGPU with "x2" in the TB3 ctrl7 column has two Thunderbolt 3 controllers.

Loopback bottleneck: do you mean video from eGPU to iGPU? That means the Link cable has DisplayPort? In that case, the link cable should be connected to the GPU in the eGPU (requires a GPU with a USB-C port). If the link is connected to the GPU then the eGPU doesn't need two TB controllers.

Mac mini (2018), Mac Pro (Early 2008), MacBook Pro (Retina, 15-inch, Mid 2015), GA-Z170X-Gaming 7, Sapphire Pulse Radeon RX 580 8GB GDDR5, Sonnet Echo Express III-D, Trebleet Thunderbolt 3 to NVMe M.2 case


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dancole42
(@dancole42)
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Joined: 3 months ago
 
Posted by: @joevt

In the buyer's guide, any eGPU with "x2" in the TB3 ctrl7 column has two Thunderbolt 3 controllers.

Loopback bottleneck: do you mean video from eGPU to iGPU? That means the Link cable has DisplayPort? In that case, the link cable should be connected to the GPU in the eGPU (requires a GPU with a USB-C port). If the link is connected to the GPU then the eGPU doesn't need two TB controllers.

The Link cable appears to be USB-C. My understanding is that the optimal setup for an eGPU is:

Laptop => TB => eGPU => External monitor

Whereas:

Laptop => TB => eGPU => TB => Laptop internal monitor

Causes a 15-20% drop in performance because of the added overhead of sending the image back over the Thunderbolt (the "loopback bottleneck"). Now, the Rift S connects to a DisplayPort, so I'd assume it would be treated as an external monitor and not have the issue.

The Oculus Link, however, as far as I know, isn't treated as an external monitor, and so my thinking is:

Laptop => TB => eGPU => eGPU's TB I/O => Oculus

Is better than:

Laptop => TB => eGPU => TB => Laptop's internal USB I/O => Oculus

Does that make sense?

Also, thanks for the link, I never noticed the TB controller column! Exactly what I was looking for.

HP Spectre x360 13" FHD i7-1065G7


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joevt
(@joevt)
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Posted by: @dancole42

The Oculus Link, however, as far as I know, isn't treated as an external monitor, and so my thinking is:

You're right. I did some reading. It does not use DisplayPort. It uses USB (like DisplayLink).

In that case, for best performance, the Oculus Link cable should be connected directly to the computer. 

If the Oculus Link cable is connected to the eGPU then you get this situation:
eGPU renders frames -> data travels from GPU to RAM over Thunderbolt -> data travels from RAM over Thunderbolt to USB port -> Oculus Link

If the Oculus Link cable is connected to the computer, then you get this situation:
eGPU renders frames -> data travels from GPU to RAM over Thunderbolt -> data travels from RAM over PCIe to USB port -> Oculus Link.

You save one trip over Thunderbolt with the latter.

I don't think there's a method to remove the "data travels from GPU to RAM over Thunderbolt" part of the process. But even if there was, you are wanting to send data from the GPU over Thunderbolt to the second Thunderbolt controller that has a USB port that the Oculus Link is connected to, so you haven't really saved any time over Thunderbolt. An eGPU with one Thunderbolt controller might be better in that case because there is no Thunderbolt between the GPU and the USB port.

Mac mini (2018), Mac Pro (Early 2008), MacBook Pro (Retina, 15-inch, Mid 2015), GA-Z170X-Gaming 7, Sapphire Pulse Radeon RX 580 8GB GDDR5, Sonnet Echo Express III-D, Trebleet Thunderbolt 3 to NVMe M.2 case


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Baptiste Fournial
(@babao)
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Joined: 2 years ago
 

And what about Nvidia Cards with a built-in USB ? I saw in the EVGA documentation that this was « Virtual-Link » ready..

formerly KFA2 GTX 1060
Now on Razer Core X, Sapphire Vega64, MacBook TB, 4C8T 2018

 
2018 13" MacBook Pro [8th,4C,U] + GTX 1060 @ 32Gbps-TB3 (Galax SNPR) + Win10 1803 [build link]  


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joevt
(@joevt)
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@babao, Oculus Link is not Virtual Link.

The best place for a USB only connection such as Oculus Link is directly to the computer.

The best place for a DisplayPort connection (including Virtual Link) is the eGPU. But Virtual Link includes USB+DisplayPort. I don't think you'll notice a difference in latency between USB from eGPU and USB from computer (but I have not seen this tested). An adapter like the Bizlink VirtualLink Interface Adapter would let you get DisplayPort from the eGPU and USB from the computer, but this adapter doesn't actually exist.

 

Mac mini (2018), Mac Pro (Early 2008), MacBook Pro (Retina, 15-inch, Mid 2015), GA-Z170X-Gaming 7, Sapphire Pulse Radeon RX 580 8GB GDDR5, Sonnet Echo Express III-D, Trebleet Thunderbolt 3 to NVMe M.2 case


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Baptiste Fournial
(@babao)
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Joined: 2 years ago
 

I saw on Oculus forums that for some people, the Oculus Quest works when plugged on the Nvidia Virtual Link, with a regular active USB3 cable (and for some others people that it didn't).

Having a eGPU, it might be great to have the video signal going only one-way through the TB3 interface.

formerly KFA2 GTX 1060
Now on Razer Core X, Sapphire Vega64, MacBook TB, 4C8T 2018

 
2018 13" MacBook Pro [8th,4C,U] + GTX 1060 @ 32Gbps-TB3 (Galax SNPR) + Win10 1803 [build link]  


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joevt
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@babao, the Nvidia Virtual Link port also supports USB and DisplayPort. If you only need a USB signal, then a connection directly to the computer would be better for latency but I don't know if you'll notice a difference. The Nvidia Virtual Link support USB 3.1 gen 2 (10 Gbps). If the device can use 10 Gbps and your computer only has USB 3.0 (5 Gbps) then the Virtual Link port might be better (bandwidth) (I am unclear about the specs of the Oculus Quest).

If the video has to be translated to USB, then you don't gain performance by having the USB connector on the eGPU (the video data has to go to the CPU to get translated to USB).

 

Mac mini (2018), Mac Pro (Early 2008), MacBook Pro (Retina, 15-inch, Mid 2015), GA-Z170X-Gaming 7, Sapphire Pulse Radeon RX 580 8GB GDDR5, Sonnet Echo Express III-D, Trebleet Thunderbolt 3 to NVMe M.2 case


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Baptiste Fournial
(@babao)
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Joined: 2 years ago
 
Posted by: @joevt

@babao, the Nvidia Virtual Link port also supports USB and DisplayPort. If you only need a USB signal, then a connection directly to the computer would be better for latency but I don't know if you'll notice a difference. The Nvidia Virtual Link support USB 3.1 gen 2 (10 Gbps). If the device can use 10 Gbps and your computer only has USB 3.0 (5 Gbps) then the Virtual Link port might be better (bandwidth) (I am unclear about the specs of the Oculus Quest).

If the video has to be translated to USB, then you don't gain performance by having the USB connector on the eGPU (the video data has to go to the CPU to get translated to USB).

 

I guess it's done by the GPU, if not, what's the point of all this ?

formerly KFA2 GTX 1060
Now on Razer Core X, Sapphire Vega64, MacBook TB, 4C8T 2018

 
2018 13" MacBook Pro [8th,4C,U] + GTX 1060 @ 32Gbps-TB3 (Galax SNPR) + Win10 1803 [build link]  


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joevt
(@joevt)
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Joined: 3 years ago
 

@babao, I suppose a GPU can do the rendering for Oculus Link but the video is sent by USB instead of DisplayPort? I am not 100% sure how it works.

 

Mac mini (2018), Mac Pro (Early 2008), MacBook Pro (Retina, 15-inch, Mid 2015), GA-Z170X-Gaming 7, Sapphire Pulse Radeon RX 580 8GB GDDR5, Sonnet Echo Express III-D, Trebleet Thunderbolt 3 to NVMe M.2 case


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