[cpu/windows] Switch to performance counters

[VihasMakwana]

Add conditional switching to performance counters for cpu/core metricset collections
This PR add an option WithPerformanceCounter, which uses performance counter for CPU data collection, when enabled.
Default behaviour will be the existing implementation.

How to use performance counters?

It's simple. Something like following:

cpu, _ := metrics.New(WithPerformanceCounter())
data, err := cpu.Fetch()

Why performance counters?

From elastic/beats#40926,

On Windows, Metricbeat measures CPU use via the Windows API call GetSystemTimes. Each metrics interval, it fetches the CPU numbers, and compares them to the previous measurement to determine CPU load during that interval. On most systems this includes CPU time "including all threads in all processes, on all processors". However, on systems with more than 64 cores, it returns only the data for the current processor group of up to 64 cores.

This is a major limitation for such systems and it leads to inconsistent data.

Testing

Test results are reported on the linked issue.

Fixes elastic/beats#40926

Note:

WithPerformanceCounter option is only effective for windows and is ineffective if used by other OS'.

[VihasMakwana]

This will be updated once elastic/elastic-agent-libs#252 is merged and released

[VihasMakwana]

PR is up for review!

[mauri870]

I assume performance counters is just a windows thing? If so, we could add a comment at the top of this function that states that it only applies to windows.

[VihasMakwana]

Yup. That's better

[cmacknz]

Putting Windows in the option name would be even more obvious.

Also, consider that we are probably going to want to make this the default once we are satisfied with it. Probably just deleting the option would work once we do that but something to consider for the near future.

[mauri870]

Reviewed again, LGTM. I'm learning quite a bit about Windows internals through your PR chain.

[leehinman]

LGTM, optional refactor.

[leehinman]

Nit. Just to improve readability and testing. I think it would be nice if Get was something like:

func Get(m *Monitor) (CPUMetrics, error) {
    if m.query == nil {
        return getUsingSystemTimes()
    }
    return getUsingPerformanceCounters(m)
}

That way it is explicit that the only thing Get does is pick which implementation to use, and it is easy to test the 2 implementations independently.

[VihasMakwana]

Got it. Thanks!