DRAM power consumption with turbostat

Julia Lawall
2022-01-30T10:27:37Z

Hello,

I was wondering whether the DRAM power consumption reported by turbostat
is reliable on recent Intel machines?

In particular, I observed that turbostat reported a high DRAM energy
comsumption on a machine (Intel 5128) with persistent memory, but where
the persistent memory was not being used. A colleague did an experiemnt
on another machine with persistent memory, and reported:

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I didn't run the test on troll but on another server equipped with PM
where I was able to reproduce the bug and by reading directly the msr
registers, I see that:
CPU Energy units = 0.00006104J
DRAM Energy units = 0.00001526J

However turbostat assumes that the DRAM Energy units is 0.00006104J when
it runs the computation to obtain Joules (hence the too-high value
returned by turbostat)

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I see the code in turbostat that just uses the CPU energy units value
(rapl_dram_energy_units_probe), but I don't know what was the MSR used to
collect the above information. Overall, I am wondering if the DRAM energy
consumption values are reliable in cases with and without persistent
memory.

thanks,
julia