// instantFromCumulativeMetric calculates the value of an instantaneous metric from two
// points of a cumulative metric, such as cpu/usage.
// The inputs are the value and timestamp of the newer cumulative datapoint,
// and a pointer to a TimePoint holding the previous cumulative datapoint.
func instantFromCumulativeMetric(value uint64, stamp time.Time, prev *store.TimePoint) (uint64, error) {
if prev == nil {
return uint64(0), fmt.Errorf("unable to calculate instant metric with nil previous TimePoint")
}
tdelta := uint64(stamp.Sub(prev.Timestamp).Nanoseconds())
if tdelta == 0 {
return uint64(0), fmt.Errorf("cumulative metric timestamps are identical")
}
vdelta := (value - prev.Value.(uint64)) * 1024
instaVal := vdelta / tdelta
prev.Value = value
prev.Timestamp = stamp
return instaVal, nil
}
// instantFromCumulativeMetric calculates the value of an instantaneous metric from two
// points of a cumulative metric, such as cpu/usage.
// The inputs are the value and timestamp of the newer cumulative datapoint,
// and a pointer to a TimePoint holding the previous cumulative datapoint.
func instantFromCumulativeMetric(value uint64, stamp time.Time, prev *store.TimePoint) (uint64, error) {
if prev == nil {
return uint64(0), fmt.Errorf("unable to calculate instant metric with nil previous TimePoint")
}
tdelta := uint64(stamp.Sub(prev.Timestamp).Nanoseconds())
if tdelta == 0 {
return uint64(0), fmt.Errorf("cumulative metric timestamps are identical")
}
// Divide metric by nanoseconds that have elapsed, multiply by 1000 to get an unsigned metric
vdelta := (value - prev.Value.(uint64)) * 1000
instaVal := vdelta / tdelta
prev.Value = value
prev.Timestamp = stamp
return instaVal, nil
}
// instantFromCumulativeMetric calculates the value of an instantaneous metric from two
// points of a cumulative metric, such as cpu/usage.
// The inputs are the value and timestamp of the newer cumulative datapoint,
// and a pointer to a TimePoint holding the previous cumulative datapoint.
func instantFromCumulativeMetric(value uint64, stamp time.Time, prev *store.TimePoint) (uint64, error) {
if prev == nil {
return uint64(0), fmt.Errorf("unable to calculate instant metric with nil previous TimePoint")
}
if !stamp.After(prev.Timestamp) {
return uint64(0), fmt.Errorf("the previous TimePoint is not earlier in time than the newer one")
}
tdelta := uint64(stamp.Sub(prev.Timestamp).Nanoseconds())
// Divide metric by nanoseconds that have elapsed, multiply by 1000 to get an unsigned metric
if value < prev.Value.(uint64) {
return uint64(0), fmt.Errorf("the provided value %d is less than the previous one %d", value, prev.Value.(uint64))
}
vdelta := (value - prev.Value.(uint64)) * 1000
instaVal := vdelta / tdelta
prev.Value = value
prev.Timestamp = stamp
return instaVal, nil
}