[NavinF]

>diminishing returns especially due to it working faster than the speed of my RAM (2667MT/s * 8 = ~21 GB/s).

That sounds kinda slow; Is there only 1 DIMM in the slots? I remember benchmarking 40GiB/s read speed on an older system that had 2 dual-rank DIMMs (4 ranks in total).

I'd expect 3200mbit/s*(64 data lines)*(2 memory channels) = ~48 GiB/s on a typical DDR4 desktop and a lot more with overclocked ram.

Great writeup either way.

[wooosh]

Yes, this is on a single 8GB 2667MHz DIMM in a laptop.

edit: For dual channel RAM, I would suspect the throughput depends on how the kernel decides to map physical memory to virtual addresses.

[adrian_b]

The memory is already mapped by the BIOS/EFI firmware, before the kernel takes control.

By default, whenever the memory modules used in all different channels have the same size, e.g. two 8 GB modules, the firmware maps the modules with interleaved addresses, to ensure a double throughput for 2 channels, or triple/quadruple/etc. for workstation/server motherboards with more memory channels.