What happens when more than 100% of pool B is allocated?

Question

What happens when more than 100% of pool B is allocated?

So my Mac Pro currently has 125% of pool B allocated. Using pool B is my Pro Display XDR plugged into my Radeon Pro Vega II Duo (x4 I believe), an Apple Afterburner Card in slot 6 (x8) and a PCIe NVMe SSD in slot 7(also x8). I understand that each pool has 16 lanes, so this is over the limit for pool B. However pool A is already at 100% from my Afterburner in slot 5 (x16). Both MPX slots have Radeon Pro Vega II Duos in them. I'm not looking for tips to fix this but I would like to know how the PCIe lanes are distributed. Or is there a way to manually distribute them? If so I would like to only distribute 4 lanes to the SSD as I can live with slower storage.

Mac Pro

Posted on Jun 27, 2020 5:43 AM

Reply

Answer 1

Jun 27, 2020 7:20 AM in response to jamesonliu2357

https://9to5mac.com/2019/07/01/expansion-slot-utility-mac-pro/

(hints that if under-configured, things might run more slowly than possible)

Install PCIe cards in your Mac Pro (2019) - Apple Support

(has a section on manually assigning bandwidth inside a pool, but does not explain whether you can move stuff between pools except by moving a card to a different slot)

Reply

Answer 2

Jun 28, 2020 10:08 AM in response to Grant Bennet-Alder

There is currently nothing plugged into the I/O card in slot 8 and Pool B remained at 125% allocation when I removed it, suggesting it is not using any PCIe bandwidth (makes sense as nothing is plugged in so no bandwidth would be needed). There is also nothing plugged into the top two Thunderbolt ports. Testing does seem to show that the Mac runs roughly the same regardless of whether Pool B is over-allocated or not but the difference with the second Afterburner is noticeable. Apple does say that up to three Afterburners can increase performance. And since I already have the second card I might as well use it.

Reply

Answer 3

Jun 27, 2020 8:08 AM in response to jamesonliu2357

Are you certain you are actually benefiting from TWO afterburner cards? I though one was enough for many streams of high-res raw video.

Regardless, it looks like the only thing pushing you over the limit is the (low speed) I/O card in slot 8. I don't think you will see many issue from this very modest over-configuration.

Reply

What happens when more than 100% of pool B is allocated?

Similar questions