As a matter of fact this is a very interesting question, and touching the world of statistics. one of my favorite subjects.
Since your cpu.usage.average values for each hour will hardly be ever exactly the same, you would need to have a value to express how close the values are together.
In the statistics world they mostly use the standard variation for this.
In the following script I use a function based on the Welford algorithm to calculate the standard variation.
The following script uses a threshold of 5 for the standard deviation to determine if the CPU percentages are "close" together, and thus indicating a rather constant CPU usage.
Play around with the threshold.
function Get-WelfordStdVar{
param([int[]]$Samples)
$n = $mean = $M2 = 0
$Samples | %{
$n++
$delta = $_ - $mean
$mean += ($delta/$n)
$M2 += ($delta*($_ - $mean))
}
if($n -lt 2){0}
else{
$M2/($n-1)
}
}
$vms = Get-VM
$stat = 'cpu.usage.average'
$start = (Get-Date).AddDays(-1)
$threshold = 5
Get-Stat -Entity $vms -Stat $stat -Start $start |
Group-Object -Property EntityId,{$_.Timestamp.Hour} | %{
New-Object PSObject -Property @{
VM = $_.Group[0].Entity.Name
Hour = $_.Group[0].Timestamp.Hour
CPU = [math]::Round(($_.Group | Where {$_.Instance -eq ''} | Measure-Object -Property Value -Average | Select -ExpandProperty Average),1)
}
} |
Group-Object VM | %{
$values = $_.Group | Sort-Object -Property Hour | %{$_.CPU}
$stdvar = Get-WelfordStdVar -Samples $values
if($stdvar -le $threshold){
$_ | Select Name,@{N='StdVar';E={[math]::Round($stdvar,2)}},@{N='CPU';E={[string]::Join('/',$values)}}
}
}
