hrtime.Since() sometimes returns negative durations #14
Description
I was running some benchmarks and started seeing impossible results (negative MB/s speeds). So upon some debugging I've found out that some of the time samples collected are negative values (where typical values could be 14-digit decimal number so it cannot be an int64 overflow).
Here is relevant code sample:
type benchmarkResult struct {
name string
packTimings []time.Duration
unpackTimings []time.Duration
packInputSize int64
packOutputSize int64
}
//... more code...
benchResult := newBenchmarkResult(e.Name())
benchResults = append(benchResults, benchResult)
//... more code...
for i := 0; i < samples_count; i++ {
var start time.Duration
var elapsed time.Duration
start = hrtime.Now()
// code that I benchmark
benchResult.packOutputSize = benchmarkee.packBuffer(packedStage2Buff,
inputBuff[:benchResult.packInputSize])
//------------- elapsed is sometimes negative for no apparent reason --------------------
elapsed = hrtime.Since(start)
benchResult.packTimings = append(benchResult.packTimings, elapsed)
//... more code...
}
//... more code...
and here is an example content of benchResult.packTimings after running this loop:
[]time.Duration len: 10, cap: 10, [
13056411500,
12958258400,
13248242400,
12969406300,
13192194100,
12935541500,
-1831576101470, // <- obviously a bad measurement
13263809300,
13024965000,
13255804100]
I use: github.com/loov/hrtime v1.0.3
I'm running this on go version go1.21.5 windows/amd64
My OS is:
Windows 10 Pro
Version 22H2
OS Build 19045.6456
If you need I can send you the code+data that produced this bug. Just let me know.
I hope you can look into this. Cheers!