srowen commented on a change in pull request #23914: [SPARK-27009][TEST] Add
Standard Deviation to benchmark results
URL: https://github.com/apache/spark/pull/23914#discussion_r261380291
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File path: core/src/test/scala/org/apache/spark/benchmark/Benchmark.scala
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@@ -158,7 +159,8 @@ private[spark] class Benchmark(
// scalastyle:on
val best = runTimes.min
val avg = runTimes.sum / runTimes.size
- Result(avg / 1000000.0, num / (best / 1000.0), best / 1000000.0)
+ val stdev = math.sqrt(runTimes.map(time => math.pow(time - avg, 2)).sum /
runTimes.size)
Review comment:
You can assume (or assert) that there was at least 1 benchmarking run, or
none of the metrics mean anything. (maybe it's already asserted)
While the sample stdev is not really defined for 1 run, "0" is fine.
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