Yes, that's what I'm suspecting too, although with higher clocked RAM, I should have somewhat more bandwidth. My DIMMs are 3200 MT, so should be running at 1600 MHz. But I saw a note (not sure where) that Infinity Fabric can run up to 2933 MT on my machine and it would run in sync with memory with DIMMs only up to 2933 MT. Unfortunately my BIOS doesn't allow to downgrade the RAM "clock" from 3200 MT to 2933, thus Ininity Fabric is running "out of sync" with my RAM.
This should mean non-ideal memory access latency at least, not sure how it affects throughput of large sequential transfers.
I'm planning to come up with some additional tests and hopefully write up a "part 2" too.
> Unfortunately my BIOS doesn't allow to downgrade the RAM "clock"
How deep are you willing to go?
The RAM clock is controlled by the memory training algorithms. They use data from the XMP, which can be edited.
The simplest is to reflash your memory sticks to alter their XMP, so the training algorithm will reach the conclusions you want. There's some Windows software to do that.
You could also implement your own MRC, something done by coreboot and the likes.
Ha, thanks for the idea! I was briefly thinking of buying 2933 "MHz" RAM for the test (as I later would put it into my other workstation that can go up to 2600 "MHz" only), but then I realized I don't have time for this right now (will do my throughput, performance stability tests first and maybe look into getting the most out of the latency later).
https://en.wikichip.org/wiki/amd/infinity_fabric