Re: [PATCH v3 3/3] Add support for RAPL MSRs in KVM/Qemu

[Anthony Harivel]

Hi Daniel,


> You don't need to access it via the /node/ hierarchy
>
> The canonical path for CPUs would be
>
>   /sys/devices/system/cpu/cpuNNN/topology
>
> The core_cpus_list file is giving you hyper-thread siblings within
> a core, which I don't think is what you want.
>
> If you're after discrete physical packages, then 'package_cpus_list'
> gives you all CPUs within a physical socket (package) I believe.
>

Yes, this could work.
However, on laptop, I've got: 
cat package_cpus_list
0-11

Where on server: 
package_cpus_list
0,2,4,6,8,10,12,14,16,18,20,22,24,26,28,30,32,34,36,38,40,42,44,46

I asked my teammate: always the same results. This is I guess due to 
either a difference in the kernel version or how the kernel is handling 
the case where there is only one package, versus the case with multiple 
packages. 

Anyway, writing a C function to handle both cases might not be easy. 

The other solution would be to loop through 
/sys/devices/system/cpu/cpuNNN/ and update a table of integer of a fixed 
size (*) where I increment table[0] for package_0 when I encounter a CPU 
that belongs to package_0 and so on. Reading 
cpuNNN/topology/physical_package_id is giving to whom package the cpu 
belongs to.

This is a bit tedious but a safer solution, I think.


(*): Maybe dynamic allocation is better ?

Thanks again for your guidance.

Regards,
Anthony