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capacity-limiter-api: avoid division in EMA #3030

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Aug 5, 2024
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capacity-limiter-api: avoid division in EMA #3030

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8 changes: 4 additions & 4 deletions ...apacity-limiter-api/src/main/java/io/servicetalk/capacity/limiter/api/LatencyTracker.java
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Original file line number Diff line number Diff line change
Expand Up @@ -61,7 +61,7 @@ public double observe(long timestampNs, final long latency) {
*/
final class EMA implements LatencyTracker {

private final double tau;
private final double invTau;
@Nullable
private final LatencyTracker calmTracker;
@Nullable
Expand All @@ -75,7 +75,7 @@ final class EMA implements LatencyTracker {
* @param halfLifeNs The decay window of the EMA.
*/
EMA(final long halfLifeNs) {
this.tau = halfLifeNs / log(2);
this.invTau = 1.0 / (halfLifeNs / log(2));
this.calmTracker = null;
this.calmRatio = null;
}
Expand All @@ -94,7 +94,7 @@ final class EMA implements LatencyTracker {
EMA(final long halfLifeNs, final LatencyTracker calmTracker,
final BiFunction<Double, Double, Float> calmRatio) {
NumberUtils.ensurePositive(halfLifeNs, "halfLifeNs");
this.tau = halfLifeNs / log(2);
this.invTau = 1.0 / (halfLifeNs / log(2));
this.calmTracker = requireNonNull(calmTracker);
this.calmRatio = requireNonNull(calmRatio);
}
Expand All @@ -112,7 +112,7 @@ public double observe(long timestampNs, final long latency) {
}
}

final double tmp = (timestampNs - lastTimeNanos) / tau;
final double tmp = (timestampNs - lastTimeNanos) * invTau;
final double w = exp(-tmp);
ewma = ewma * w + latency * (1d - w);
lastTimeNanos = timestampNs;
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