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Confused, ALL TB3 ports on 2017 13”Macbook Pro with Touchbar have FULL PCI bandwidth.  

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MilkyWayne
(@milkywayne)
New Member
Joined: 3 weeks ago
Posts: 2
April 15, 2019 6:22 am  

As many build guides suggest, when setting up eGPU with 2016 and 2017 13” MacbookPro with Touchbar, always use the left TB3 ports as right ones have reduced PCI Express Bandwidth.

However, I noticed by accident that all of the TB3 ports on my 17 13” MBP have full PCI Bandwidth.

  1. When plug-in any TB3 port, macOS shows PCI Lane X16 and PCI Speed of 8.0GT/s.
  2. I ran some LuxMark test in macOS, the result shows no different between left and right ports.
  3. I also ran 3D mark in bootcamp, the Time Spy Benchmark shows no different between left and right ports either.

Now, I am really confused, is it mean I can plug-in any TB3 port on my MBP to use the eGPU with out any performance depreciation?

Many thanks.

2017 13” Macbook Pro with TouchBar, i5-7276U/Intel Iris 650/16G RAM/256GB SSD
Razer Core X
Sapphire Vega 56 Pulse
Dell P2715Q
Logitech MX Master Mouse and Filco Bluetooth Keyboard


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theitsage
(@itsage)
Famed Member Admin
Joined: 2 years ago
Posts: 3817
April 15, 2019 1:17 pm  

The PCI tree in macOS System Information doesn't always report accurate PCIe link width for eGPU. A better tool for confirming Thunderbolt 3 bandwidth is CL!ng in macOS. Here's the screen capture of a full x4 PCIe connection [Paged column].

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MilkyWayne
(@milkywayne)
New Member
Joined: 3 weeks ago
Posts: 2
April 15, 2019 2:20 pm  
Posted by: theitsage

The PCI tree in macOS System Information doesn't always report accurate PCIe link width for eGPU. A better tool for confirming Thunderbolt 3 bandwidth is CL!ng in macOS. Here's the screen capture of a full x4 PCIe connection [Paged column].

Thanks! CL!ng do solve my problem instantly.

It shows the right port on my 2017 MBP has 2/3 of the memory bandwidth to the left port, clearly both right port do not run in full speed.

Although I still don't understand why a reduced bandwidth connection will not affect the benchmark, it seems using the left port is a smart choice.

Thx again, really appreciated. 

2017 13” Macbook Pro with TouchBar, i5-7276U/Intel Iris 650/16G RAM/256GB SSD
Razer Core X
Sapphire Vega 56 Pulse
Dell P2715Q
Logitech MX Master Mouse and Filco Bluetooth Keyboard


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OliverB
(@oliverb)
Noble Member
Joined: 6 months ago
Posts: 1047
April 15, 2019 2:37 pm  
Posted by: MilkyWayne

Although I still don't understand why a reduced bandwidth connection will not affect the benchmark, it seems using the left port is a smart choice.

@milkywayne
This depends highly on the benchmark. Synthetic Benchmarks like Unigine Valley or Time Spy are highly optimized and use only a small part of your H2D Bandwidth. Thus they will not change with reduced bandwidth. This may change with games and applications.

In any case the H2D Bandwidth is massively overrated. A GTX1080Ti on x4 PCIE lanes still beats most other cards on x16 PCIE lanes.

This post was modified 1 week ago

2018 15" MBP & 2015 13" MBP connected to RTX2080Ti GTX1080Ti GTX1080 Vega56 RX580 R9-290 GTX680


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