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Subject [GitHub] [spark] vanzin commented on a change in pull request #26058: [SPARK-10614][core] Add monotonic time to Clock interface.
Date Tue, 08 Oct 2019 20:21:52 GMT
vanzin 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_r332714350
 
 

 ##########
 File path: core/src/main/scala/org/apache/spark/ExecutorAllocationManager.scala
 ##########
 @@ -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:
   That is interesting, but according to this:
   
       http://btorpey.github.io/blog/2014/02/18/clock-sources-in-linux/
   
   `CLOCK_MONOTONIC` uses RDTSC (or RDTSCP when available), which solves that problem. The
preferred one (RDTSCP) seems to be available in all modern CPUs. So, `CLOCK_MONOTONIC` actually
fulfills the requirements of the `nanoTime()` API (that the source of time is consistent).
   
   (The AMD K8 mentioned in your comment, which came out more than 10 years ago, is where
RDTSCP was added.)

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