MaxGekk commented on a change in pull request #26058: [SPARK-10614][core] Add
monotonic time to Clock interface.
URL: https://github.com/apache/spark/pull/26058#discussion_r332707004
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File path: core/src/main/scala/org/apache/spark/ExecutorAllocationManager.scala
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@@ -288,7 +288,7 @@ private[spark] class ExecutorAllocationManager(
}
// Update executor target number only after initializing flag is unset
- updateAndSyncNumExecutorsTarget(clock.getTimeMillis())
+ updateAndSyncNumExecutorsTarget(clock.nanoTime())
Review comment:
`System.nanoTime()` can use `clock_gettime(CLOCK_MONOTONIC, ...)` on Linux:
http://hg.openjdk.java.net/jdk8/jdk8/hotspot/file/tip/src/os/linux/vm/os_linux.cpp#l1453
`CLOCK_MONOTONIC` is based on the Time Stamp Counter
(https://en.wikipedia.org/wiki/Time_Stamp_Counter). Its synchronization across
CPU cores depends on CPU architecture, for example: _"AMD processors up to the
K8 core always incremented the time-stamp counter every clock cycle.[6] Thus,
power management features were able to change the number of increments per
second, and the values could get out of sync between different cores or
processors in the same system."_
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