// Copyright 2015 Google Inc. All Rights Reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// Utility methods to calculate percentiles.
package summary
import (
"fmt"
"math"
"sort"
info "github.com/google/cadvisor/info/v2"
)
const secondsToMilliSeconds = 1000
const milliSecondsToNanoSeconds = 1000000
const secondsToNanoSeconds = secondsToMilliSeconds * milliSecondsToNanoSeconds
type Uint64Slice []uint64
func (s Uint64Slice) Len() int { return len(s) }
func (s Uint64Slice) Swap(i, j int) { s[i], s[j] = s[j], s[i] }
func (s Uint64Slice) Less(i, j int) bool { return s[i] < s[j] }
// Get percentile of the provided samples. Round to integer.
func (s Uint64Slice) GetPercentile(d float64) uint64 {
if d < 0.0 || d > 1.0 {
return 0
}
count := s.Len()
if count == 0 {
return 0
}
sort.Sort(s)
n := float64(d * (float64(count) + 1))
idx, frac := math.Modf(n)
index := int(idx)
percentile := float64(s[index-1])
if index > 1 && index < count {
percentile += frac * float64(s[index]-s[index-1])
}
return uint64(percentile)
}
type mean struct {
// current count.
count uint64
// current mean.
Mean float64
}
func (m *mean) Add(value uint64) {
m.count++
if m.count == 1 {
m.Mean = float64(value)
return
}
c := float64(m.count)
v := float64(value)
m.Mean = (m.Mean*(c-1) + v) / c
}
type Percentile interface {
Add(info.Percentiles)
AddSample(uint64)
GetAllPercentiles() info.Percentiles
}
type resource struct {
// list of samples being tracked.
samples Uint64Slice
// average from existing samples.
mean mean
// maximum value seen so far in the added samples.
max uint64
}
// Adds a new percentile sample.
func (r *resource) Add(p info.Percentiles) {
if !p.Present {
return
}
if p.Max > r.max {
r.max = p.Max
}
r.mean.Add(p.Mean)
// Selecting 90p of 90p :(
r.samples = append(r.samples, p.Ninety)
}
// Add a single sample. Internally, we convert it to a fake percentile sample.
func (r *resource) AddSample(val uint64) {
sample := info.Percentiles{
Present: true,
Mean: val,
Max: val,
Fifty: val,
Ninety: val,
NinetyFive: val,
}
r.Add(sample)
}
// Get max, average, and 90p from existing samples.
func (r *resource) GetAllPercentiles() info.Percentiles {
p := info.Percentiles{}
p.Mean = uint64(r.mean.Mean)
p.Max = r.max
p.Fifty = r.samples.GetPercentile(0.5)
p.Ninety = r.samples.GetPercentile(0.9)
p.NinetyFive = r.samples.GetPercentile(0.95)
p.Present = true
return p
}
func NewResource(size int) Percentile {
return &resource{
samples: make(Uint64Slice, 0, size),
mean: mean{count: 0, Mean: 0},
}
}
// Return aggregated percentiles from the provided percentile samples.
func GetDerivedPercentiles(stats []*info.Usage) info.Usage {
cpu := NewResource(len(stats))
memory := NewResource(len(stats))
for _, stat := range stats {
cpu.Add(stat.Cpu)
memory.Add(stat.Memory)
}
usage := info.Usage{}
usage.Cpu = cpu.GetAllPercentiles()
usage.Memory = memory.GetAllPercentiles()
return usage
}
// Calculate part of a minute this sample set represent.
func getPercentComplete(stats []*secondSample) (percent int32) {
numSamples := len(stats)
if numSamples > 1 {
percent = 100
timeRange := stats[numSamples-1].Timestamp.Sub(stats[0].Timestamp).Nanoseconds()
// allow some slack
if timeRange < 58*secondsToNanoSeconds {
percent = int32((timeRange * 100) / 60 * secondsToNanoSeconds)
}
}
return
}
// Calculate cpurate from two consecutive total cpu usage samples.
func getCPURate(latest, previous secondSample) (uint64, error) {
elapsed := latest.Timestamp.Sub(previous.Timestamp).Nanoseconds()
if elapsed < 10*milliSecondsToNanoSeconds {
return 0, fmt.Errorf("elapsed time too small: %d ns: time now %s last %s", elapsed, latest.Timestamp.String(), previous.Timestamp.String())
}
if latest.Cpu < previous.Cpu {
return 0, fmt.Errorf("bad sample: cumulative cpu usage dropped from %d to %d", latest.Cpu, previous.Cpu)
}
// Cpurate is calculated in cpu-milliseconds per second.
cpuRate := (latest.Cpu - previous.Cpu) * secondsToMilliSeconds / uint64(elapsed)
return cpuRate, nil
}
// Returns a percentile sample for a minute by aggregating seconds samples.
func GetMinutePercentiles(stats []*secondSample) info.Usage {
lastSample := secondSample{}
cpu := NewResource(len(stats))
memory := NewResource(len(stats))
for _, stat := range stats {
if !lastSample.Timestamp.IsZero() {
cpuRate, err := getCPURate(*stat, lastSample)
if err != nil {
continue
}
cpu.AddSample(cpuRate)
memory.AddSample(stat.Memory)
} else {
memory.AddSample(stat.Memory)
}
lastSample = *stat
}
percent := getPercentComplete(stats)
return info.Usage{
PercentComplete: percent,
Cpu: cpu.GetAllPercentiles(),
Memory: memory.GetAllPercentiles(),
}
}