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

["Daniel P. Berrangé" <berrange@redhat.com>]

On Thu, Mar 14, 2024 at 09:26:53AM +0100, Anthony Harivel wrote:
> 
> 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.

Both are the same data format - it is a list of ranges. In the
laptop example, there's only a single range to parse. In the
server example there are many ranges but since each range is
only 1 cpu, it has collapsed the ranges to the single CPU id.

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

Approximately

  * Read the whole file with g_get_file_contents
  * Use  g_strsplit(data, ",", 0) to get a list of ranges
  * Iterate over the return list of ranges and g_strsplit(range, "-", 2);
      - The returned list should be either a single element (if there was
         no '-'), or a pair of elements (if there was a N-M)


With regards,
Daniel
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