Hacker News Reader

Comment by wmf | Hacker News Reader

Won’t the timing of each chipset on each board need to be painstakingly individually configured to avoid latency from a “default” profile used in all chips (which inherently vary between every batch)?

No, because PCIe works completely differently from RAM. PCIe is a packet-based protocol that's very latency-tolerant. (Multi-lane PCIe links may require deskew but that's a standard feature that has existed all along.) I think it was Marcan who tunneled PCIe over RS-232 and the chips didn't even notice.

View on HN

This isn't really true for PCIe 4 and beyond. For example, if you use a competently manufactured PCIe 3 riser in a PCIe 4 GPU configuration then VGA will fail to POST more times than it succeeds (on the order of successfully booting 1/10), if it POSTs at all. Given how expensive PCIe 4 risers are most people choose to downgrade to PCIe 3 in the firmware settings.

Are you sure this isn’t because of the tightened electrical tolerances for PCIe’s physical layer, not the protocol it’s self?

That's signal integrity not latency though.

Well the chipset also handles shuttling RAM channels..

No. You appear to have a fundamentally flawed understanding of the system at hand.

Perhaps. 16 years out from AMD ram/ cpu channel optimization. If the chipset isn’t handling RAM channels what component is?

The DRAM controller has been on the CPU socket since AMD's Opteron/Athlon 64 (2003) and Intel's Nehalem first-gen Core i5/i7 products (2008). AMD's recent migration toward multiple chiplets on the CPU package has not changed the direct connection between DRAM and the CPU socket.

>AMD's recent migration toward multiple chiplets on the CPU package has not changed the direct connection between DRAM and the CPU socket

This is true. However with the MCH off-chip and worst case inter core latency comparable a DRAM refresh cycle, AMD could in theory move the MCH away from the socket and see no major performance penalty.

Not to mention the Zen 2 IO die is just a cut-down version of X570, or maybe it is the other way around heh?

Reply on news.ycombinator.com