Does 1 Thunderbolt 3 port have enough juice for external graphics AND a 10gbe?

[jonathan murphy]

Looking at a lot of mobile workstations with only 1 thunderbolt 3 port. I want to get an external graphics solution when they are released later this year. Would 1 thunderbolt 3 port allow for an external graphics card AND a 10gpe connection to connect to my raid? Or do I need to look for the horned unicorn that has 2 TB3 ports?

 

[Jeff Kilgroe]

Thunderbolt 3 has 40Gbps of throughput. There is also some overhead with that and in the current implementation used by Dell and a few of the currently available systems with TB3, we are only getting about 34Gbps maximum with the PCIe host lane allotment. Thunderbolt also provides its bandwidth through aggregate channels. It is able to divide out into 4 channels at 10Gbps each. So you can have one channel provided 10GbE while still retaining the remainder for PCIe/graphics expansion. Different signal formats (Ethernet, PCIe, USB, DisplayPort, HDMI, etc..) require separate channelization on the TB interface and sometimes also additional switching. So, if you connect a PCIe expansion unit (external graphics solution) along with a TB to 10GbE device and a TB to USB device, then that graphics solution is already relegated to running at 1/2 its potential bandwidth.

Now the next question is how much bandwidth is needed for external graphics? Hmmm.... Hard to say. Initial details are somewhat sketchy, but it looks like external GPUs are going to be stacked with a lot of RAM and additional functionality to overcome the bandwidth limitation. For gamers this works, as there's more memory on the eGPU to pre-load tons of data, models, textures, whatever. In terms of computational use, most computational GPU tasks usually don't tax the bandwidth. However, video I/O tasks can run out of bandwidth by the time we send 4K+ sized frames to a GPU and back.

Ultimately, I think I would rather go for a multi-GPU system and know I'm going to get better performance than to try and add on a GPU, in the midst of other peripherals. OTOH, current MacBook Pro or similar systems with dual Thunderbolt 2 ports are being used effectively with an external Rocket X card on one port and a RAID on the other port. The same can be accomplished with a single Thunderbolt 3 port, providing the same bandwidth to those devices. Ideally we'd like a system with at least two of those Thunderbolt 3 ports. Also keep in mind that while current TB3 ports have about ~35Gbps real-world throughput, a PCIe 3.0 X16 slot for current GPUs has nearly 4X that.

 

[jonathan murphy]

Thunderbolt 3 has 40Gbps of throughput. There is also some overhead with that and in the current implementation used by Dell and a few of the currently available systems with TB3, we are only getting about 34Gbps maximum with the PCIe host lane allotment. Thunderbolt also provides its bandwidth through aggregate channels. It is able to divide out into 4 channels at 10Gbps each. So you can have one channel provided 10GbE while still retaining the remainder for PCIe/graphics expansion. Different signal formats (Ethernet, PCIe, USB, DisplayPort, HDMI, etc..) require separate channelization on the TB interface and sometimes also additional switching. So, if you connect a PCIe expansion unit (external graphics solution) along with a TB to 10GbE device and a TB to USB device, then that graphics solution is already relegated to running at 1/2 its potential bandwidth.

Now the next question is how much bandwidth is needed for external graphics? Hmmm.... Hard to say. Initial details are somewhat sketchy, but it looks like external GPUs are going to be stacked with a lot of RAM and additional functionality to overcome the bandwidth limitation. For gamers this works, as there's more memory on the eGPU to pre-load tons of data, models, textures, whatever. In terms of computational use, most computational GPU tasks usually don't tax the bandwidth. However, video I/O tasks can run out of bandwidth by the time we send 4K+ sized frames to a GPU and back.

Ultimately, I think I would rather go for a multi-GPU system and know I'm going to get better performance than to try and add on a GPU, in the midst of other peripherals. OTOH, current MacBook Pro or similar systems with dual Thunderbolt 2 ports are being used effectively with an external Rocket X card on one port and a RAID on the other port. The same can be accomplished with a single Thunderbolt 3 port, providing the same bandwidth to those devices. Ideally we'd like a system with at least two of those Thunderbolt 3 ports. Also keep in mind that while current TB3 ports have about ~35Gbps real-world throughput, a PCIe 3.0 X16 slot for current GPUs has nearly 4X that.

Thanks so much for that info! That is extremely helpful. Would a laptop with 2 TB3 ports like the HP zbook studio 15 both (for lack of a better term) be completely separate from one another? What I mean is will they be pulling from the same pcie slot inside the computer? Would they slow one another down if you had them both doing some intense output? (external graphics etc.)

 

[jonathan murphy]

Also would something like the Alienware 15 r2 be a viable solution with its proprietary graphics amplifer (external graphics system)? It also has a TB3 port so that could be a nice setup if the x4 lane isn't too much of a performance hit

 

[Steve Strickler]

Anyone making a TB3 PCI card? Thx

 

[Jeff Kilgroe]

Difficult to say on the bandwidth of dual TB3 ports. Each TB header can support two ports sharing the available bandwidth. So far, Apple has been the only one to consistently put dual TB ports on their notebooks with discrete bandwidth per port. TB3 being integrated with USB 3.5 + USB-C standard connectors as well as being easier to license and implement should help adoption in the PC market -- hopefully we'll have lots of options soon. Dell is really the only one to be offering real TB3 at the moment and they jumped the gun somewhat, but it's here.

As for the Alienware with their graphics amplifier, I'm not sure how viable that is. It seems somewhat limited and isn't exactly seen as a proper GPU for CUDA/ OpenCL acceleration, so I don't know if it's really a viable solution for anything but supporting compatible games at the moment.

ASUS and a few others are making TB3 PCIe cards, however just like TB2 add-in cards, they are matched to work with compatible systems. We won't be able to buy a TB3 card and drop it into any system. And all the current motherboards out there that support TB2 cards on an X4 interface will not offer any reason to upgrade that card to TB3 as there isn't enough PCIe lanes/bandwidth to back it. We'll have to wait for the next round of motherboard and TB3 add-in cards.