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compute actual sample rate for profile export #26

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merged 1 commit into from
Oct 9, 2023
Merged

compute actual sample rate for profile export #26

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15 changes: 13 additions & 2 deletions fgprof.go
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Original file line number Diff line number Diff line change
Expand Up @@ -6,6 +6,7 @@ package fgprof
import (
"fmt"
"io"
"math"
"runtime"
"sort"
"strings"
Expand Down Expand Up @@ -37,16 +38,19 @@ func Start(w io.Writer, format Format) func() error {
const hz = 99
ticker := time.NewTicker(time.Second / hz)
stopCh := make(chan struct{})

prof := &profiler{}
profile := newWallclockProfile()

var sampleCount int64

go func() {
defer ticker.Stop()

for {
select {
case <-ticker.C:
sampleCount++

stacks := prof.GoroutineProfile()
profile.Add(stacks)
case <-stopCh:
Expand All @@ -59,7 +63,14 @@ func Start(w io.Writer, format Format) func() error {
stopCh <- struct{}{}
endTime := time.Now()
profile.Ignore(prof.SelfFrames()...)
return profile.Export(w, format, hz, startTime, endTime)

// Compute actual sample rate in case, due to performance issues, we
// were not actually able to sample at the given hz. Converting
// everything to float avoids integers being rounded in the wrong
// direction and improves the correctness of times in profiles.
duration := endTime.Sub(startTime)
actualHz := float64(sampleCount) / (float64(duration) / 1e9)
return profile.Export(w, format, int(math.Round(actualHz)), startTime, endTime)
}
}

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