Test on Threadripper 2990WX and fix SMT

[steckdenis]

On almost every Linux kernel, core i and i+1 are the two threads of a single physical core. Power consumption statistics can therefore be obtained by reading the MSRs or cores 0, 2, 4, ..., 60, 62.

This pull request makes rapl report proper power consumption on my machine. By the way, this tool is absolutely amazing! I have been looking for something like this for a year and a half!

[Asheboy]

I agree with this. @djselbeck can this be merged?

[bachandi]

On a Threadripper PRO 3975WX (64 threads) with 5.11 Kernel core i and i + 32 are the two threads of a single physical core so there would be some logic needed to check which core numbering is needed instead of just changing to i*2

BTW great tool.

[c10l]

On a AMD Ryzen 7 PRO 4750G with Radeon Graphics (8 cores, 16 threads), i and i + 8 are the 2 threads of the same core.

[maximilianpalm]

Could you use /proc/cpuinfo or similar to accurately determine the core configuration? This way, you can first detect whether SMT is active. If needed, you could then get the mapping of the logical to the physical cores.

On a Ryzen 9 5950X (32 threads) with Ubuntu 22.04.3 LTS (6.2.0-33-generic) and SMT enabled I get i and i + 16:

$ egrep "core id|processor" /proc/cpuinfo
processor	: 0
core id		: 0
processor	: 1
core id		: 1
[...]
processor	: 14
core id		: 14
processor	: 15
core id		: 15

processor	: 16
core id		: 0
processor	: 17
core id		: 1
[...]
processor	: 30
core id		: 14
processor	: 31
core id		: 15

(Skipped lines and added line break for readability)