From e26606acfd52a623fc617ae42584c19ecbde6592 Mon Sep 17 00:00:00 2001
From: Sean Chittenden <sean@chittenden.org>
Date: Fri, 17 Jun 2016 12:13:53 -0700
Subject: [PATCH] Memoize the CPU stats.  Error if CPU fingerprinting fails.

---
 client/fingerprint/cpu.go | 65 ++++++++++++------------------------
 helper/stats/cpu.go       | 70 ++++++++++++++++++++++++++++-----------
 2 files changed, 72 insertions(+), 63 deletions(-)

diff --git a/client/fingerprint/cpu.go b/client/fingerprint/cpu.go
index 8c04cd951..bd5d43165 100644
--- a/client/fingerprint/cpu.go
+++ b/client/fingerprint/cpu.go
@@ -5,8 +5,8 @@ import (
 	"log"
 
 	"github.com/hashicorp/nomad/client/config"
+	"github.com/hashicorp/nomad/helper/stats"
 	"github.com/hashicorp/nomad/nomad/structs"
-	"github.com/shirou/gopsutil/cpu"
 )
 
 // CPUFingerprint is used to fingerprint the CPU
@@ -22,55 +22,32 @@ func NewCPUFingerprint(logger *log.Logger) Fingerprint {
 }
 
 func (f *CPUFingerprint) Fingerprint(cfg *config.Config, node *structs.Node) (bool, error) {
-	cpuInfo, err := cpu.Info()
-	if err != nil {
-		f.logger.Println("[WARN] Error reading CPU information:", err)
+	if err := stats.Init(); err != nil {
+		f.logger.Printf("[FATAL] fingerprint.cpu: unable to obtain CPU information: %v", err)
 		return false, err
 	}
 
-	// Assume all CPUs found have same Model and MHz. If cpu.Info()
-	// returns nil above, this loop is still safe.
-	var mhz float64
-	var modelName string
-	for _, c := range cpuInfo {
-		mhz = c.Mhz
-		modelName = c.ModelName
-		break
-	}
-
-	// Allow for a little precision slop
-	if mhz < 1.0 {
-		f.logger.Println("[WARN] fingerprint.cpu: Unable to obtain the CPU Mhz")
-	} else {
-		node.Attributes["cpu.frequency"] = fmt.Sprintf("%.6f", mhz)
-		f.logger.Printf("[DEBUG] fingerprint.cpu: frequency: %02.1f MHz", mhz)
-	}
-
-	var numCores int
-	if numCores, err = cpu.Counts(true); err != nil {
-		numCores = 1
-		f.logger.Println("[WARN] Unable to obtain the number of CPUs, defaulting to %d CPU", numCores)
-	}
-
-	if numCores > 0 {
-		node.Attributes["cpu.numcores"] = fmt.Sprintf("%d", numCores)
-		f.logger.Printf("[DEBUG] fingerprint.cpu: core count: %d", numCores)
-	}
-
-	if mhz > 0 && numCores > 0 {
-		tc := float64(numCores) * mhz
-		node.Attributes["cpu.totalcompute"] = fmt.Sprintf("%.6f", tc)
-
-		if node.Resources == nil {
-			node.Resources = &structs.Resources{}
-		}
-
-		node.Resources.CPU = int(tc)
-	}
-
+	modelName := stats.CPUModelName()
 	if modelName != "" {
 		node.Attributes["cpu.modelname"] = modelName
 	}
 
+	mhz := stats.CPUMHzPerCore()
+	node.Attributes["cpu.frequency"] = fmt.Sprintf("%.6f", mhz)
+	f.logger.Printf("[DEBUG] fingerprint.cpu: frequency: %02.1f MHz", mhz)
+
+	numCores := stats.CPUNumCores()
+	node.Attributes["cpu.numcores"] = fmt.Sprintf("%d", numCores)
+	f.logger.Printf("[DEBUG] fingerprint.cpu: core count: %d", numCores)
+
+	tt := stats.TotalTicksAvailable()
+	node.Attributes["cpu.totalcompute"] = fmt.Sprintf("%.6f", tt)
+
+	if node.Resources == nil {
+		node.Resources = &structs.Resources{}
+	}
+
+	node.Resources.CPU = int(tt)
+
 	return true, nil
 }
diff --git a/helper/stats/cpu.go b/helper/stats/cpu.go
index 0c6373dfd..624252ff3 100644
--- a/helper/stats/cpu.go
+++ b/helper/stats/cpu.go
@@ -1,30 +1,62 @@
 package stats
 
 import (
-	"github.com/shirou/gopsutil/cpu"
+	"fmt"
 	"sync"
+
+	"github.com/shirou/gopsutil/cpu"
 )
 
 var (
-	clkSpeed  float64
-	ticksLock sync.Mutex
+	cpuMhzPerCore float64
+	cpuModelName  string
+	cpuNumCores   int
+	cpuTotalTicks float64
+
+	onceLer sync.Once
 )
 
-// TotalTicksAvailable calculates the total frequency available across all cores
-func TotalTicksAvailable() float64 {
-	ticksLock.Lock()
-	defer ticksLock.Unlock()
-	if clkSpeed == 0.0 {
-		var cpuInfo []cpu.InfoStat
-		var err error
-
-		var totalTicks float64
-		if cpuInfo, err = cpu.Info(); err == nil {
-			for _, cpu := range cpuInfo {
-				totalTicks += cpu.Mhz
-			}
-			clkSpeed = totalTicks
+func Init() error {
+	var err error
+	onceLer.Do(func() {
+		if cpuNumCores, err = cpu.Counts(true); err != nil {
+			err = fmt.Errorf("Unable to determine the number of CPU cores available: %v", err)
+			return
 		}
-	}
-	return clkSpeed
+
+		var cpuInfo []cpu.InfoStat
+		if cpuInfo, err = cpu.Info(); err != nil {
+			err = fmt.Errorf("Unable to obtain CPU information: %v", err)
+			return
+		}
+
+		for _, cpu := range cpuInfo {
+			cpuModelName = cpu.ModelName
+			cpuMhzPerCore = cpu.Mhz
+			break
+		}
+		cpuTotalTicks = float64(cpuNumCores) * cpuMhzPerCore
+	})
+	return err
+}
+
+// CPUModelName returns the number of CPU cores available
+func CPUNumCores() int {
+	return cpuNumCores
+}
+
+// CPUMHzPerCore returns the MHz per CPU core
+func CPUMHzPerCore() float64 {
+	return cpuMhzPerCore
+}
+
+// CPUModelName returns the model name of the CPU
+func CPUModelName() string {
+	return cpuModelName
+}
+
+// TotalTicksAvailable calculates the total frequency available across all
+// cores
+func TotalTicksAvailable() float64 {
+	return cpuTotalTicks
 }