From 2143fa2ab7b7ec6d56aa8eaf1b0a90b96bea7f0a Mon Sep 17 00:00:00 2001
From: Preetha Appan <preetha@hashicorp.com>
Date: Thu, 27 Sep 2018 23:44:01 -0500
Subject: [PATCH] Use scheduler config from state store to enable/disable
 preemption

---
 scheduler/scheduler.go         |  3 +++
 scheduler/stack.go             | 14 +++++++++-----
 scheduler/system_sched_test.go |  6 ++++++
 3 files changed, 18 insertions(+), 5 deletions(-)

diff --git a/scheduler/scheduler.go b/scheduler/scheduler.go
index b9f0f5e3a..bd921a788 100644
--- a/scheduler/scheduler.go
+++ b/scheduler/scheduler.go
@@ -88,6 +88,9 @@ type State interface {
 	// LatestDeploymentByJobID returns the latest deployment matching the given
 	// job ID
 	LatestDeploymentByJobID(ws memdb.WatchSet, namespace, jobID string) (*structs.Deployment, error)
+
+	// SchedulerConfig returns config options for the scheduler
+	SchedulerConfig() (uint64, *structs.SchedulerConfiguration, error)
 }
 
 // Planner interface is used to submit a task allocation plan.
diff --git a/scheduler/stack.go b/scheduler/stack.go
index 6be27c5e2..d9ae982b4 100644
--- a/scheduler/stack.go
+++ b/scheduler/stack.go
@@ -109,10 +109,9 @@ func NewGenericStack(batch bool, ctx Context) *GenericStack {
 	rankSource := NewFeasibleRankIterator(ctx, s.distinctPropertyConstraint)
 
 	// Apply the bin packing, this depends on the resources needed
-	// by a particular task group. Only enable eviction for the service
-	// scheduler as that logic is expensive.
-	evict := !batch
-	s.binPack = NewBinPackIterator(ctx, rankSource, evict, 0)
+	// by a particular task group.
+
+	s.binPack = NewBinPackIterator(ctx, rankSource, false, 0)
 
 	// Apply the job anti-affinity iterator. This is to avoid placing
 	// multiple allocations on the same node for this job.
@@ -287,7 +286,12 @@ func NewSystemStack(ctx Context) *SystemStack {
 	// Apply the bin packing, this depends on the resources needed
 	// by a particular task group. Enable eviction as system jobs are high
 	// priority.
-	s.binPack = NewBinPackIterator(ctx, rankSource, true, 0)
+	_, schedConfig, _ := s.ctx.State().SchedulerConfig()
+	enablePreemption := false
+	if schedConfig != nil {
+		enablePreemption = schedConfig.EnablePreemption
+	}
+	s.binPack = NewBinPackIterator(ctx, rankSource, enablePreemption, 0)
 
 	// Apply score normalization
 	s.scoreNorm = NewScoreNormalizationIterator(ctx, s.binPack)
diff --git a/scheduler/system_sched_test.go b/scheduler/system_sched_test.go
index d2cf1f5f8..a190d113a 100644
--- a/scheduler/system_sched_test.go
+++ b/scheduler/system_sched_test.go
@@ -242,6 +242,9 @@ func TestSystemSched_ExhaustResources(t *testing.T) {
 	node := mock.Node()
 	noErr(t, h.State.UpsertNode(h.NextIndex(), node))
 
+	// Enable Preemption
+	h.State.SchedulerSetConfig(h.NextIndex(), &structs.SchedulerConfiguration{EnablePreemption: true})
+
 	// Create a service job which consumes most of the system resources
 	svcJob := mock.Job()
 	svcJob.TaskGroups[0].Count = 1
@@ -1573,6 +1576,9 @@ func TestSystemSched_Preemption(t *testing.T) {
 		nodes = append(nodes, node)
 	}
 
+	// Enable Preemption
+	h.State.SchedulerSetConfig(h.NextIndex(), &structs.SchedulerConfiguration{EnablePreemption: true})
+
 	// Create some low priority batch jobs and allocations for them
 	// One job uses a reserved port
 	job1 := mock.BatchJob()