Does it matter which RAM Channels I populate on a 4-channel optimized EPYC?

[mstum]

I’m currently waiting for an EPYC 7282 arrive, which will go on an ASRock Rack ROMED8-2T board, also waiting for that.

The 7282 is one of the EPYCs with half the memory bandwidth because only 2 CCXes are populated, but I’m not clear on whether it matters which memory slots I populate. The Board has only 1 DIMM per Channel, but I wonder if the CCX’es are connected to the I/O die equally, or if there are RAM Slots that are connected to one of the CCX’es while others have to go through the I/O die (kinda like 2nd Gen Threadripper).

Assuming 4 DIMMs, do I have to figure out where to put them (is there a way in Linux or FreeBSD to see if RAM is connected to a CPU Core even if it just shows up as a single NUMA node?) or can I just put them in whatever slots I want? (As said, the board only has 1 DIMM per channnel, so I don’t have to worry about putting 2 DIMMs on the same Channel)

[GigaBusterEXE]

memory controllers are separate from CCXes, the dimm slots are connected to the memory controller which divvy’s up the bandwidth to the CCXes
if the board only has 4 dimms populate all 4

[w.meri]

Page 21 of the ROMED8-2T manual says populate A1, B1, G1, and H1 if using four DIMMs.

[Dynamic_Gravity]

When in doubt, read the manual.