metrics: prevent negative counter from iowait decrease

.changelog/18835.txt

@@ -0,0 +1,3 @@
+```release-note:bug
+metrics: Fixed a bug where CPU counters could report errors for negative values
+```

client/hoststats/host.go

@@ -273,7 +273,7 @@ func (h *HostCpuStatsCalculator) Calculate(times cpu.TimesStat) (idle float64, u
 	currentIdle := times.Idle
 	currentUser := times.User
 	currentSystem := times.System
-	currentTotal := times.Total()
+	currentTotal := times.Total() // this is Idle + currentBusy
 	currentBusy := times.User + times.System + times.Nice + times.Iowait + times.Irq +
 		times.Softirq + times.Steal + times.Guest + times.GuestNice
 
@@ -284,16 +284,16 @@ func (h *HostCpuStatsCalculator) Calculate(times cpu.TimesStat) (idle float64, u
 	total = ((currentBusy - h.prevBusy) / deltaTotal) * 100
 
 	// Protect against any invalid values
-	if math.IsNaN(idle) || math.IsInf(idle, 0) {
+	if math.IsNaN(idle) || math.IsInf(idle, 0) || idle < 0.0 {
 		idle = 100.0
 	}
-	if math.IsNaN(user) || math.IsInf(user, 0) {
+	if math.IsNaN(user) || math.IsInf(user, 0) || user < 0.0 {
 		user = 0.0
 	}
-	if math.IsNaN(system) || math.IsInf(system, 0) {
+	if math.IsNaN(system) || math.IsInf(system, 0) || system < 0.0 {
 		system = 0.0
 	}
-	if math.IsNaN(total) || math.IsInf(total, 0) {
+	if math.IsNaN(total) || math.IsInf(total, 0) || total < 0.0 {
 		total = 0.0
 	}
 

client/hoststats/host_test.go

@@ -7,6 +7,7 @@ import (
 	"testing"
 
 	"github.com/shirou/gopsutil/v3/cpu"
+	"github.com/shoenig/test/must"
 )
 
 func TestHostCpuStatsCalculator_Nan(t *testing.T) {
@@ -20,16 +21,34 @@ func TestHostCpuStatsCalculator_Nan(t *testing.T) {
 	calculator.Calculate(times)
 	idle, user, system, total := calculator.Calculate(times)
 
-	if idle != 100.0 {
-		t.Errorf("idle: Expected: %f, Got %f", 100.0, idle)
-	}
-	if user != 0.0 {
-		t.Errorf("user: Expected: %f, Got %f", 0.0, user)
-	}
-	if system != 0.0 {
-		t.Errorf("system: Expected: %f, Got %f", 0.0, system)
+	must.Eq(t, 100.0, idle, must.Sprint("unexpected idle stats"))
+	must.Eq(t, 0.0, user, must.Sprint("unexpected user stats"))
+	must.Eq(t, 0.0, system, must.Sprint("unexpected system stats"))
+	must.Eq(t, 0.0, total, must.Sprint("unexpected total stats"))
+}
+
+func TestHostCpuStatsCalculator_DecreasedIOWait(t *testing.T) {
+	times := cpu.TimesStat{
+		CPU:    "cpu0",
+		User:   20000,
+		Nice:   100,
+		System: 9000,
+		Idle:   370000,
+		Iowait: 700,
 	}
-	if total != 0.0 {
-		t.Errorf("total: Expected: %f, Got %f", 0.0, total)
+
+	calculator := NewHostCpuStatsCalculator()
+	calculator.Calculate(times)
+
+	times = cpu.TimesStat{
+		CPU:    "cpu0",
+		User:   20000,
+		Nice:   100,
+		System: 9000,
+		Idle:   380000,
+		Iowait: 600,
 	}
+
+	_, _, _, total := calculator.Calculate(times)
+	must.GreaterEq(t, 0.0, total, must.Sprint("total must never be negative"))
 }