Windows CPU times can add up to > 100%

[conorbranagan]

We're collecting PercentUserTime and PercentIdleTime from Win32_PerfFormattedData_PerfOS_Processor which shouldn't ever add up to more than 100%, but it seems like it does.

Maybe we need to use a different metric other than PercentIdleTime?

[MisterRayCo]

[remh]

We should try if this can be reproduced with psutil, and maybe use psutil to solve that issue.

[bunelr]

At first I thought that it could be related to this issue that was on psutil: (broken windows api where cpu times is sometimes decreasing) but I think that maybe we're not getting PercentUserTime correctly:

From msdn doc,
PercentUserTime and PercentPrivilegedTime are Percentage of non-idle processor time and we report then directly so we may have been over-reporting them ( not dividing them by PercentProcessorTime )

I'm a bit worried that on the docs linked PercentIdleTime is described as the 'sample interval that the disk was idle' but it's probably just a typo, given that the basis of the data here report it as the processor Idle time.

I'll try correcting the values and see if we get better results

[bunelr]

After checking, it seems that we're getting the points correctly because PercentUserTime and PercentPrivilegedTime always sum up to roughly PercentProcessorTime so they must be a percentage of the total time and there is no need for correction.

Reporting system.cpu.idle as 100 - PercentProcessorTime should give better results (I build one check reporting this way and haven't seen any value getting over 100) but it still feels like it isn't a proper solution. I'll try deducing the values from PerfRawData instead to see if we can get saner results

[remh]

Should we just switch to psutil to get these metrics on Windows ? How does psutil get them ?

[bunelr]

Psutil calls another system function GetSystemTimes with which it gets kerneltime, usertime and idletime, waits, and then call this function again, which allows him to deduce the percentages of time spent in user mode, system mode and idle mode.
An issue is that we also get system.cpu.interrupt that is not available with psutil.

Update on using 100-PercentProcessorTime instead of PercentIdleTime: it also gets >100 spikes

I'll check collecting the value we can with psutils and keeping the wmi solution for system.cpu.interrupt

[conorbranagan]

👍