Ngone51 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_r303005949
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File path: core/src/main/scala/org/apache/spark/scheduler/TaskSetManager.scala
##########
@@ -330,128 +303,65 @@ private[spark] class TaskSetManager(
}
}
- /**
- * Return a speculative task for a given executor if any are available. The
task should not have
- * an attempt running on this host, in case the host is slow. In addition,
the task should meet
- * the given locality constraint.
- */
- // Labeled as protected to allow tests to override providing speculative
tasks if necessary
- protected def dequeueSpeculativeTask(execId: String, host: String, locality:
TaskLocality.Value)
- : Option[(Int, TaskLocality.Value)] =
- {
- speculatableTasks.retain(index => !successful(index)) // Remove finished
tasks from set
-
- def canRunOnHost(index: Int): Boolean = {
- !hasAttemptOnHost(index, host) &&
- !isTaskBlacklistedOnExecOrNode(index, execId, host)
- }
-
- if (!speculatableTasks.isEmpty) {
- // Check for process-local tasks; note that tasks can be process-local
- // on multiple nodes when we replicate cached blocks, as in Spark
Streaming
- for (index <- speculatableTasks if canRunOnHost(index)) {
- val prefs = tasks(index).preferredLocations
- val executors = prefs.flatMap(_ match {
- case e: ExecutorCacheTaskLocation => Some(e.executorId)
- case _ => None
- })
- if (executors.contains(execId)) {
- speculatableTasks -= index
- return Some((index, TaskLocality.PROCESS_LOCAL))
- }
- }
-
- // Check for node-local tasks
- if (TaskLocality.isAllowed(locality, TaskLocality.NODE_LOCAL)) {
- for (index <- speculatableTasks if canRunOnHost(index)) {
- val locations = tasks(index).preferredLocations.map(_.host)
- if (locations.contains(host)) {
- speculatableTasks -= index
- return Some((index, TaskLocality.NODE_LOCAL))
- }
- }
- }
-
- // Check for no-preference tasks
- if (TaskLocality.isAllowed(locality, TaskLocality.NO_PREF)) {
- for (index <- speculatableTasks if canRunOnHost(index)) {
- val locations = tasks(index).preferredLocations
- if (locations.size == 0) {
- speculatableTasks -= index
- return Some((index, TaskLocality.PROCESS_LOCAL))
- }
- }
- }
-
- // Check for rack-local tasks
- if (TaskLocality.isAllowed(locality, TaskLocality.RACK_LOCAL)) {
- for (rack <- sched.getRackForHost(host)) {
- for (index <- speculatableTasks if canRunOnHost(index)) {
- val racks =
tasks(index).preferredLocations.map(_.host).flatMap(sched.getRackForHost)
- if (racks.contains(rack)) {
- speculatableTasks -= index
- return Some((index, TaskLocality.RACK_LOCAL))
- }
- }
- }
- }
-
- // Check for non-local tasks
- if (TaskLocality.isAllowed(locality, TaskLocality.ANY)) {
- for (index <- speculatableTasks if canRunOnHost(index)) {
- speculatableTasks -= index
- return Some((index, TaskLocality.ANY))
- }
- }
- }
-
- None
- }
-
/**
* Dequeue a pending task for a given node and return its index and locality
level.
* Only search for tasks matching the given locality constraint.
*
* @return An option containing (task index within the task set, locality,
is speculative?)
*/
private def dequeueTask(execId: String, host: String, maxLocality:
TaskLocality.Value)
- : Option[(Int, TaskLocality.Value, Boolean)] =
- {
- for (index <- dequeueTaskFromList(execId, host,
getPendingTasksForExecutor(execId))) {
- return Some((index, TaskLocality.PROCESS_LOCAL, false))
+ : Option[(Int, TaskLocality.Value, Boolean)] = {
+ // Tries to schedule a regular task first; if it returns None, then
schedules
+ // a speculative task
+ dequeueTaskHelper(execId, host, maxLocality, false).orElse(
+ dequeueTaskHelper(execId, host, maxLocality, true))
+ }
+
+ private def dequeueTaskHelper(
+ execId: String,
+ host: String,
+ maxLocality: TaskLocality.Value,
+ speculative: Boolean): Option[(Int, TaskLocality.Value, Boolean)] = {
+ if (speculative && speculatableTasks.isEmpty) {
+ return None
+ }
+ val pendingTaskSetToUse = if (speculative) pendingSpeculatableTasks else
pendingTasks
+ def dequeue(list: ArrayBuffer[Int]): Option[Int] = {
+ dequeueTaskFromList(execId, host, list, speculative)
+ }
+
+ dequeue(pendingTaskSetToUse.forExecutor.getOrElse(execId,
ArrayBuffer())).foreach { index =>
+ return Some((index, TaskLocality.PROCESS_LOCAL, speculative))
}
if (TaskLocality.isAllowed(maxLocality, TaskLocality.NODE_LOCAL)) {
- for (index <- dequeueTaskFromList(execId, host,
getPendingTasksForHost(host))) {
- return Some((index, TaskLocality.NODE_LOCAL, false))
+ dequeue(pendingTaskSetToUse.forHost.getOrElse(host,
ArrayBuffer())).foreach { index =>
+ return Some((index, TaskLocality.NODE_LOCAL, speculative))
}
}
+ // Look for noPref tasks after NODE_LOCAL for minimize cross-rack traffic
if (TaskLocality.isAllowed(maxLocality, TaskLocality.NO_PREF)) {
- // Look for noPref tasks after NODE_LOCAL for minimize cross-rack traffic
- for (index <- dequeueTaskFromList(execId, host,
pendingTasksWithNoPrefs)) {
- return Some((index, TaskLocality.PROCESS_LOCAL, false))
+ dequeue(pendingTaskSetToUse.noPrefs).foreach { index =>
+ return Some((index, TaskLocality.NO_PREF, speculative))
Review comment:
Why this change to `NO_PREF` ? Doesn't this changed original behavior ?
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