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Disable fused multiply-subtract optimizations on activator calculations #8341

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merged 1 commit into from Jun 16, 2020
Merged

Disable fused multiply-subtract optimizations on activator calculations #8341

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7 changes: 4 additions & 3 deletions pkg/autoscaler/scaling/autoscaler.go
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Expand Up @@ -254,9 +254,10 @@ func (a *Autoscaler) Scale(ctx context.Context, now time.Time) ScaleResult {
excessBCF = 0
// numAct stays 1, only needed to scale from 0.
case a.deciderSpec.TargetBurstCapacity > 0:
totCap := float64(originalReadyPodsCount) * a.deciderSpec.TotalValue
excessBCF = math.Floor(totCap - observedPanicValue -
a.deciderSpec.TargetBurstCapacity)
// Extra float64 cast disables fused multiply-subtract to force identical behavior on
// all platforms. See floating point section in https://golang.org/ref/spec#Operators.
totCap := float64(float64(originalReadyPodsCount) * a.deciderSpec.TotalValue)
excessBCF = math.Floor(totCap - a.deciderSpec.TargetBurstCapacity - observedPanicValue)
numAct = int32(math.Max(MinActivators,
math.Ceil((totCap+a.deciderSpec.TargetBurstCapacity)/a.deciderSpec.ActivatorCapacity)))
case a.deciderSpec.TargetBurstCapacity == -1:
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4 changes: 3 additions & 1 deletion pkg/autoscaler/scaling/autoscaler_test.go
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Expand Up @@ -70,7 +70,9 @@ func TestAutoscalerNoDataNoAutoscale(t *testing.T) {
}

func expectedEBC(totCap, targetBC, recordedConcurrency, numPods float64) int32 {
return int32(math.Floor(totCap/targetUtilization*numPods - targetBC - recordedConcurrency))
// Extra float64 cast disables fused multiply-subtract to force identical behavior on
// all platforms. See floating point section in https://golang.org/ref/spec#Operators.
return int32(math.Floor(float64(totCap/targetUtilization*numPods) - targetBC - recordedConcurrency))
}

func expectedNA(a *Autoscaler, numP float64) int32 {
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