address comment

nomad/blocked_evals.go

@@ -147,7 +147,9 @@ func (b *BlockedEvals) Block(eval *structs.Evaluation) {
 	}
 
 	// Check if the eval missed an unblock while it was in the scheduler at an
-	// older index.
+	// older index. The scheduler could have been invoked with a snapshot of
+	// state that was prior to additional capacity being added or allocations
+	// becoming terminal.
 	if b.missedUnblock(eval) {
 		// Just re-enqueue the eval immediately
 		b.evalBroker.Enqueue(eval)
@@ -258,11 +260,6 @@ func (b *BlockedEvals) unblock(computedClass string, index uint64) {
 		return
 	}
 
-	// Store the index in which the unblock happened. We use this on subsequent
-	// block calls in case the evaluation was in the scheduler when a trigger
-	// occured.
-	b.unblockIndexes[computedClass] = index
-
 	// Every eval that has escaped computed node class has to be unblocked
 	// because any node could potentially be feasible.
 	var unblocked []*structs.Evaluation

nomad/leader.go

@@ -11,6 +11,13 @@ import (
 	"github.com/hashicorp/serf/serf"
 )
 
+const (
+	// failedEvalUnblockInterval is the interval at which failed evaluations are
+	// unblocked to re-enter the scheduler. A failed evaluation occurs under
+	// high contention when the schedulers plan does not make progress.
+	failedEvalUnblockInterval = 1 * time.Minute
+)
+
 // monitorLeadership is used to monitor if we acquire or lose our role
 // as the leader in the Raft cluster. There is some work the leader is
 // expected to do, so we must react to changes
@@ -346,11 +353,11 @@ func (s *Server) reapDupBlockedEvaluations(stopCh chan struct{}) {
 
 // periodicUnblockFailedEvals periodically unblocks failed, blocked evaluations.
 func (s *Server) periodicUnblockFailedEvals(stopCh chan struct{}) {
-	ticker := time.NewTimer(1 * time.Minute)
+	ticker := time.NewTimer(failedEvalUnblockInterval)
+	defer ticker.Stop()
 	for {
 		select {
 		case <-stopCh:
-			ticker.Stop()
 			return
 		case <-ticker.C:
 			// Unblock the failed allocations

scheduler/generic_sched_test.go

@@ -543,7 +543,7 @@ func TestServiceSched_EvaluateBlockedEval_Finished(t *testing.T) {
 	// Ensure the eval has no spawned blocked eval
 	if len(h.Evals) != 1 {
 		t.Fatalf("bad: %#v", h.Evals)
-		if h.Evals[0].SpawnedBlockedEval != "" {
+		if h.Evals[0].BlockedEval != "" {
 			t.Fatalf("bad: %#v", h.Evals[0])
 		}
 	}