nomad: use CPU count to determine pool size

nomad/leader.go

@@ -101,8 +101,9 @@ func (s *Server) establishLeadership(stopCh chan struct{}) error {
 	// Disable workers to free half the cores for use in the plan queue and
 	// evaluation broker
 	if numWorkers := len(s.workers); numWorkers > 1 {
-		// Disabling half the workers frees half the CPUs.
-		for i := 0; i < numWorkers/2; i++ {
+		// Disabling 3/4 of the workers frees CPU for raft and the
+		// plan applier which uses 1/2 the cores.
+		for i := 0; i < (3 * numWorkers / 4); i++ {
 			s.workers[i].SetPause(true)
 		}
 	}

nomad/plan_apply.go

@@ -2,6 +2,7 @@ package nomad
 
 import (
 	"fmt"
+	"runtime"
 	"time"
 
 	"github.com/armon/go-metrics"
@@ -42,7 +43,13 @@ func (s *Server) planApply() {
 	// holds an optimistic state which includes that plan application.
 	var waitCh chan struct{}
 	var snap *state.StateSnapshot
-	pool := NewEvaluatePool(workerPoolSize, workerPoolBufferSize)
+
+	// Setup a worker pool with half the cores, with at least 1
+	poolSize := runtime.NumCPU() / 2
+	if poolSize == 0 {
+		poolSize = 1
+	}
+	pool := NewEvaluatePool(poolSize, workerPoolBufferSize)
 	defer pool.Shutdown()
 
 	for {

nomad/plan_apply_pool.go

@@ -6,9 +6,6 @@ import (
 )
 
 const (
-	// workerPoolSize is the size of the worker pool
-	workerPoolSize = 2
-
 	// workerPoolBufferSize is the size of the buffers used to push
 	// request to the workers and to collect the responses. It should
 	// be large enough just to keep things busy

nomad/plan_apply_test.go

@@ -10,6 +10,11 @@ import (
 	"github.com/hashicorp/raft"
 )
 
+const (
+	// workerPoolSize is the size of the worker pool
+	workerPoolSize = 2
+)
+
 // planWaitFuture is used to wait for the Raft future to complete
 func planWaitFuture(future raft.ApplyFuture) (uint64, error) {
 	if err := future.Error(); err != nil {