Re:Ask HN: Resources for General Purpose GPU development on ...
by jsheard on Wednesday December 25, 2024 @02:50PM
(#42510738)
Note that the Mac Pros I/O is heavily oversubscribed so you can't just add it all up and expect to get that much bandwidth all at once. The system has two x16 slots and four x8 slots for a total of 64 lanes on paper, but the SOC only has 32 PCIe lanes to share between all of those, plus the integrated I/O and SSDs.
There's three PCIe "domains" in the current Mac Pro, all of the integrated I/O and one of the x8 slots are connected to a PCIe switch with an x8 connection to the SOC, both x16 slots and three x8 slots are connected to a PCIe switch with an x16 connection to the SOC, and the SSDs use the remaining 8 SOC lanes.
It's kind of a weird system because they kept the same PCIe slot layout as the prior Intel version despite having fewer lanes to go around (the Xeons had 48 lanes).
There's three PCIe "domains" in the current Mac Pro, all of the integrated I/O and one of the x8 slots are connected to a PCIe switch with an x8 connection to the SOC, both x16 slots and three x8 slots are connected to a PCIe switch with an x16 connection to the SOC, and the SSDs use the remaining 8 SOC lanes.
It's kind of a weird system because they kept the same PCIe slot layout as the prior Intel version despite having fewer lanes to go around (the Xeons had 48 lanes).