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_r261232628
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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:
Not that it really matters, but `(time - avg) * (time - avg)` is fine here
and faster than pow.
Super nit but I'd suggest it's more reasonable to use the sample rather than
population stdev: divide by `runTimes.size - 1`. I suppose this means also
checking that there are at least 2 runs.
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