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// Copyright 2017 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package benchstat
import (
"fmt"
"golang.org/x/perf/internal/stats"
)
// A Table is a table for display in the benchstat output.
type Table struct {
Metric string
OldNewDelta bool // is this an old-new-delta table?
Configs []string
Groups []string
Rows []*Row
}
// A Row is a table row for display in the benchstat output.
type Row struct {
Benchmark string // benchmark name
Group string // group name
Scaler Scaler // formatter for stats means
Metrics []*Metrics // columns of statistics
Delta string // formatted percent change
Note string // additional information
Change int // +1 better, -1 worse, 0 unchanged
}
// Tables returns tables comparing the benchmarks in the collection.
func (c *Collection) Tables() []*Table {
deltaTest := c.DeltaTest
if deltaTest == nil {
deltaTest = UTest
}
alpha := c.Alpha
if alpha == 0 {
alpha = 0.05
}
// Update statistics.
for _, m := range c.Metrics {
m.computeStats()
}
var tables []*Table
key := Key{}
for _, key.Unit = range c.Units {
table := new(Table)
table.Configs = c.Configs
table.Groups = c.Groups
table.Metric = metricOf(key.Unit)
table.OldNewDelta = len(c.Configs) == 2
for _, key.Group = range c.Groups {
for _, key.Benchmark = range c.Benchmarks[key.Group] {
row := &Row{Benchmark: key.Benchmark}
if len(c.Groups) > 1 {
// Show group headers if there is more than one group.
row.Group = key.Group
}
for _, key.Config = range c.Configs {
m := c.Metrics[key]
if m == nil {
row.Metrics = append(row.Metrics, new(Metrics))
continue
}
row.Metrics = append(row.Metrics, m)
if row.Scaler == nil {
row.Scaler = NewScaler(m.Mean, m.Unit)
}
}
// If there are only two configs being compared, add stats.
if table.OldNewDelta {
k0 := key
k0.Config = c.Configs[0]
k1 := key
k1.Config = c.Configs[1]
old := c.Metrics[k0]
new := c.Metrics[k1]
// If one is missing, omit row entirely.
// TODO: Control this better.
if old == nil || new == nil {
continue
}
pval, testerr := deltaTest(old, new)
row.Delta = "~"
if testerr == stats.ErrZeroVariance {
row.Note = "(zero variance)"
} else if testerr == stats.ErrSampleSize {
row.Note = "(too few samples)"
} else if testerr == stats.ErrSamplesEqual {
row.Note = "(all equal)"
} else if testerr != nil {
row.Note = fmt.Sprintf("(%s)", testerr)
} else if pval < alpha {
pct := ((new.Mean / old.Mean) - 1.0) * 100.0
row.Delta = fmt.Sprintf("%+.2f%%", pct)
if pct < 0 == (table.Metric != "speed") { // smaller is better, except speeds
row.Change = +1
} else {
row.Change = -1
}
}
if row.Note == "" && pval != -1 {
row.Note = fmt.Sprintf("(p=%0.3f n=%d+%d)", pval, len(old.RValues), len(new.RValues))
}
}
table.Rows = append(table.Rows, row)
}
}
if len(table.Rows) > 0 {
if c.AddGeoMean {
addGeomean(c, table, key.Unit, table.OldNewDelta)
}
tables = append(tables, table)
}
}
return tables
}
// metricOf returns the name of the metric with the given unit.
func metricOf(unit string) string {
switch unit {
case "ns/op":
return "time/op"
case "B/op":
return "alloc/op"
case "MB/s":
return "speed"
default:
return unit
}
}
// addGeomean adds a "geomean" row to the table,
// showing the geometric mean of all the benchmarks.
func addGeomean(c *Collection, t *Table, unit string, delta bool) {
row := &Row{Benchmark: "[Geo mean]"}
key := Key{Unit: unit}
geomeans := []float64{}
maxCount := 0
for _, key.Config = range c.Configs {
var means []float64
for _, key.Group = range c.Groups {
for _, key.Benchmark = range c.Benchmarks[key.Group] {
m := c.Metrics[key]
// Omit 0 values from the geomean calculation,
// as these either make the geomean undefined
// or zero (depending on who you ask). This
// typically comes up with things like
// allocation counts, where it's fine to just
// ignore the benchmark.
if m != nil && m.Mean != 0 {
means = append(means, m.Mean)
}
}
}
if len(means) > maxCount {
maxCount = len(means)
}
if len(means) == 0 {
row.Metrics = append(row.Metrics, new(Metrics))
delta = false
} else {
geomean := stats.GeoMean(means)
geomeans = append(geomeans, geomean)
if row.Scaler == nil {
row.Scaler = NewScaler(geomean, unit)
}
row.Metrics = append(row.Metrics, &Metrics{
Unit: unit,
Mean: geomean,
})
}
}
if maxCount <= 1 {
// Only one benchmark contributed to this geomean.
// Since the geomean is the same as the benchmark
// result, don't bother outputting it.
return
}
if delta {
row.Delta = fmt.Sprintf("%+.2f%%", ((geomeans[1]/geomeans[0])-1.0)*100.0)
}
t.Rows = append(t.Rows, row)
}