MBP 16", XDR and TB3 question

[ChromeCrescendo]

I am thinking of purchasing the MBP 16" along with the XDR Display

However, the MBP 16" uses two busses for the 4 TB3 ports

Does that mean that the second TB3 port on the side where the XDR is connected will have less utility than normal?

Additionally, will the MBP 16" graphics be slowed down due to having to run the XDR?

Thank you.

 

[joevt]

I am thinking of purchasing the MBP 16" along with the XDR Display

However, the MBP 16" uses two busses for the 4 TB3 ports

Does that mean that the second TB3 port on the side where the XDR is connected will have less utility than normal?

Additionally, will the MBP 16" graphics be slowed down due to having to run the XDR?

I've never seen a benchmark that shows a performance loss when connecting many displays or large displays.

The MacBook Pro 16-inch has a 5300M or 5500M (AMD Navi GPU) which supports Display Stream Compression (DSC) so 6K only requires a single DisplayPort connection using HBR2 link rate (like what 4K would use without DSC). You can connect a second display to the same Thunderbolt bus in this case if you like.

Considering the worst case, an older MacBook Pro that does not support DSC, the 6K display would require two HBR3 connections (only one such display per Thunderbolt bus). The second Thunderbolt port should be completely free for a Thunderbolt dock or storage device or USB device. I haven't seen a benchmark showing loss of performance from one Thunderbolt port when the other Thunderbolt port is doing dual 4K or single 6K. Actually, I tried it now on a MacMini 2018 with dual 4K from one port of a Thunderbolt bus and a Thunderbolt device connected to the other port and the device was able to receive 2600 MB/s which is near the limit of PCIe traffic over Thunderbolt.

A single Thunderbolt port has a max of 22 Gbps for PCIe traffic (2750 MB/s). I once tried raiding two Thunderbolt 3 ports but could only get 2800 MB/s which is considerably less than the 31.5 Gbps that you would expect from a PCIe 3.0 x4 device (3938 MB/s without overhead, typically 3500 MB/s).

PCIe bandwidth is shared between the two ports of a Thunderbolt bus. So if you're not using the USB of the XDR (5 Gbps) then the other port should have the full 22 Gbps remaining.

GPU and CPU temperatures may be higher which could cause slower performance? But that would be true for any display you connect.

 

[ChromeCrescendo]

I've never seen a benchmark that shows a performance loss when connecting many displays or large displays.

The MacBook Pro 16-inch has a 5300M or 5500M (AMD Navi GPU) which supports Display Stream Compression (DSC) so 6K only requires a single DisplayPort connection using HBR2 link rate (like what 4K would use without DSC). You can connect a second display to the same Thunderbolt bus in this case if you like.

Considering the worst case, an older MacBook Pro that does not support DSC, the 6K display would require two HBR3 connections (only one such display per Thunderbolt bus). The second Thunderbolt port should be completely free for a Thunderbolt dock or storage device or USB device. I haven't seen a benchmark showing loss of performance from one Thunderbolt port when the other Thunderbolt port is doing dual 4K or single 6K. Actually, I tried it now on a MacMini 2018 with dual 4K from one port of a Thunderbolt bus and a Thunderbolt device connected to the other port and the device was able to receive 2600 MB/s which is near the limit of PCIe traffic over Thunderbolt.

A single Thunderbolt port has a max of 22 Gbps for PCIe traffic (2750 MB/s). I once tried raiding two Thunderbolt 3 ports but could only get 2800 MB/s which is considerably less than the 31.5 Gbps that you would expect from a PCIe 3.0 x4 device (3938 MB/s without overhead, typically 3500 MB/s).

PCIe bandwidth is shared between the two ports of a Thunderbolt bus. So if you're not using the USB of the XDR (5 Gbps) then the other port should have the full 22 Gbps remaining.

GPU and CPU temperatures may be higher which could cause slower performance? But that would be true for any display you connect.

Thank you - so, in reality, TB3 does not reach the advertised 40Gbps?

I have not owned a laptop in many years so switching from a late-2015 27" iMac to a laptop is a "scary" proposition, especially reading these forums about fan noise and excessive heat

 

[joevt]

Thank you - so, in reality, TB3 does not reach the advertised 40Gbps?

I have not owned a laptop in many years so switching from a late-2015 27" iMac to a laptop is a "scary" proposition, especially reading these forums about fan noise and excessive heat

PCIe traffic can use up to 22 Gbps over Thunderbolt. The rest can be used by up to two DisplayPort streams over Thunderbolt. DisplayPort has higher precedence. For example, an Apple Pro Display XDR can take up to 36 Gbps (on an older MacBook Pro that doesn't support DSC) leaving only 4 Gbps left for PCIe communication to the USB controller of the display.