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stackalloc in separate method #2374

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Mar 25, 2024
Merged

stackalloc in separate method #2374

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34 changes: 24 additions & 10 deletions src/BenchmarkDotNet/Engines/Engine.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -167,12 +167,9 @@ public Measurement RunIteration(IterationData data)
if (EngineEventSource.Log.IsEnabled())
EngineEventSource.Log.IterationStart(data.IterationMode, data.IterationStage, totalOperations);

Span<byte> stackMemory = randomizeMemory ? stackalloc byte[random.Next(32)] : Span<byte>.Empty;

// Measure
var clock = Clock.Start();
action(invokeCount / unrollFactor);
var clockSpan = clock.GetElapsed();
var clockSpan = randomizeMemory
? MeasureWithRandomMemory(action, invokeCount / unrollFactor)
: Measure(action, invokeCount / unrollFactor);

if (EngineEventSource.Log.IsEnabled())
EngineEventSource.Log.IterationStop(data.IterationMode, data.IterationStage, totalOperations);
Expand All @@ -191,9 +188,29 @@ public Measurement RunIteration(IterationData data)
if (measurement.IterationStage == IterationStage.Jitting)
jittingMeasurements.Add(measurement);

return measurement;
}

// This is in a separate method, because stackalloc can affect code alignment,
// resulting in unexpected measurements on some AMD cpus,
// even if the stackalloc branch isn't executed. (#2366)
[MethodImpl(MethodImplOptions.NoInlining)]
private unsafe ClockSpan MeasureWithRandomMemory(Action<long> action, long invokeCount)
{
byte* stackMemory = stackalloc byte[random.Next(32)];
var clockSpan = Measure(action, invokeCount);
Consume(stackMemory);
return clockSpan;
}

return measurement;
[MethodImpl(MethodImplOptions.NoInlining)]
private unsafe void Consume(byte* _) { }

private ClockSpan Measure(Action<long> action, long invokeCount)
{
var clock = Clock.Start();
action(invokeCount);
return clock.GetElapsed();
}

private (GcStats, ThreadingStats, double) GetExtraStats(IterationData data)
Expand Down Expand Up @@ -225,9 +242,6 @@ public Measurement RunIteration(IterationData data)
return (gcStats, threadingStats, exceptionsStats.ExceptionsCount / (double)totalOperationsCount);
}

[MethodImpl(MethodImplOptions.NoInlining)]
private void Consume(in Span<byte> _) { }

private void RandomizeManagedHeapMemory()
{
// invoke global cleanup before global setup
Expand Down
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