squito commented on a change in pull request #23677: [SPARK-26755][SCHEDULER] :
Optimize Spark Scheduler to dequeue speculative tasks…
URL: https://github.com/apache/spark/pull/23677#discussion_r299576627
##########
File path: core/src/main/scala/org/apache/spark/scheduler/TaskSetManager.scala
##########
@@ -336,37 +327,30 @@ private[spark] class TaskSetManager(
private def dequeueTaskFromList(
execId: String,
host: String,
- list: ArrayBuffer[Int]): Option[Int] = {
- var indexOffset = list.size
- while (indexOffset > 0) {
- indexOffset -= 1
- val index = list(indexOffset)
- if (!isTaskBlacklistedOnExecOrNode(index, execId, host)) {
- // This should almost always be list.trimEnd(1) to remove tail
- list.remove(indexOffset)
- if (copiesRunning(index) == 0 && !successful(index)) {
- return Some(index)
+ list: ArrayBuffer[Int],
+ speculative: Boolean = false): Option[Int] = {
+ if (speculative) {
+ if (!list.isEmpty) {
+ for (index <- list) {
+ if (!isTaskBlacklistedOnExecOrNode(index, execId, host) &&
+ !hasAttemptOnHost(index, host)) {
+ // This should almost always be list.trimEnd(1) to remove tail
+ list -= index
+ if (!successful(index)) {
+ return Some(index)
+ }
+ }
}
}
- }
- None
- }
-
- /**
- * Dequeue a pending speculative task from the given list and return its
index. Runs similar
- * to the method 'dequeueTaskFromList' with additional constraints. Return
None if the
- * list is empty.
- */
- private def dequeueSpeculativeTaskFromList(
- execId: String,
- host: String,
- list: HashSet[Int]): Option[Int] = {
- if (!list.isEmpty) {
- for (index <- list) {
- if (!isTaskBlacklistedOnExecOrNode(index, execId, host) &&
!hasAttemptOnHost(index, host)) {
+ } else {
+ var indexOffset = list.size
+ while (indexOffset > 0) {
+ indexOffset -= 1
+ val index = list(indexOffset)
+ if (!isTaskBlacklistedOnExecOrNode(index, execId, host)) {
// This should almost always be list.trimEnd(1) to remove tail
- list -= index
- if (!successful(index)) {
+ list.remove(indexOffset)
+ if (copiesRunning(index) == 0 && !successful(index)) {
Review comment:
again, can these be combined more? There is a small logical difference
here, but seems that can be pushed down. Otherwise the differences are
confusing (and even sometimes wrong -- eg. for speculative tasks, you're
scanning from the front of the list, so the comment about removing tail is
incorrect).
```scala
var indexOffset = list.size
while (indexOffset > 0) {
indexOffset -= 1
val index = list(indexOffset)
if (!isTaskBlacklistedOnExecOrNode(index, execId, host) &&
!(speculative && hasAttemptOnHost(index, host))) {
// This should almost always be list.trimEnd(1) to remove tail
list.remove(indexOffset)
if ((copiesRunning(index) == 0 || speculative) &&
!successful(index)) {
return Some(index)
}
}
}
None
```
(I'm also wondering if we need `copiesRunning <= 1` even with speculation,
since you've got multiple lists now, will need to step through that carefully
and make sure there is a test)
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