Fix CPU system plugin gets stuck after system suspend (#3342)

(cherry picked from commit f5a9d1bc75)

CHANGELOG.md

@@ -5,6 +5,7 @@
 - [#3327](https://github.com/influxdata/telegraf/issues/3327): Fix container name filters in docker input.
 - [#3321](https://github.com/influxdata/telegraf/issues/3321): Fix snmpwalk address format in leofs input.
 - [#3329](https://github.com/influxdata/telegraf/issues/3329): Fix case sensitivity issue in sqlserver query.
+- [#3342](https://github.com/influxdata/telegraf/pull/3342): Fix CPU input plugin stuck after suspend on Linux.
 
 ## v1.4.2 [2017-10-10]
 

plugins/inputs/system/cpu.go

@@ -96,7 +96,8 @@ func (s *CPUStats) Gather(acc telegraf.Accumulator) error {
 		totalDelta := total - lastTotal
 
 		if totalDelta < 0 {
-			return fmt.Errorf("Error: current total CPU time is less than previous total CPU time")
+			err = fmt.Errorf("Error: current total CPU time is less than previous total CPU time")
+			break
 		}
 
 		if totalDelta == 0 {
@@ -126,7 +127,7 @@ func (s *CPUStats) Gather(acc telegraf.Accumulator) error {
 		s.lastStats[cts.CPU] = cts
 	}
 
-	return nil
+	return err
 }
 
 func totalCpuTime(t cpu.TimesStat) float64 {

plugins/inputs/system/cpu_test.go

@@ -184,3 +184,72 @@ func TestCPUCountIncrease(t *testing.T) {
 	err = cs.Gather(&acc)
 	require.NoError(t, err)
 }
+
+// TestCPUTimesDecrease tests that telegraf continue to works after
+// CPU times decrease, which seems to occur when Linux system is suspended.
+func TestCPUTimesDecrease(t *testing.T) {
+	var mps MockPS
+	defer mps.AssertExpectations(t)
+	var acc testutil.Accumulator
+
+	cts := cpu.TimesStat{
+		CPU:    "cpu0",
+		User:   18,
+		Idle:   80,
+		Iowait: 2,
+	}
+
+	cts2 := cpu.TimesStat{
+		CPU:    "cpu0",
+		User:   38, // increased by 20
+		Idle:   40, // decreased by 40
+		Iowait: 1,  // decreased by 1
+	}
+
+	cts3 := cpu.TimesStat{
+		CPU:    "cpu0",
+		User:   56,  // increased by 18
+		Idle:   120, // increased by 80
+		Iowait: 3,   // increased by 2
+	}
+
+	mps.On("CPUTimes").Return([]cpu.TimesStat{cts}, nil)
+
+	cs := NewCPUStats(&mps)
+
+	cputags := map[string]string{
+		"cpu": "cpu0",
+	}
+
+	err := cs.Gather(&acc)
+	require.NoError(t, err)
+
+	// Computed values are checked with delta > 0 becasue of floating point arithmatic
+	// imprecision
+	assertContainsTaggedFloat(t, &acc, "cpu", "time_user", 18, 0, cputags)
+	assertContainsTaggedFloat(t, &acc, "cpu", "time_idle", 80, 0, cputags)
+	assertContainsTaggedFloat(t, &acc, "cpu", "time_iowait", 2, 0, cputags)
+
+	mps2 := MockPS{}
+	mps2.On("CPUTimes").Return([]cpu.TimesStat{cts2}, nil)
+	cs.ps = &mps2
+
+	// CPU times decreased. An error should be raised
+	err = cs.Gather(&acc)
+	require.Error(t, err)
+
+	mps3 := MockPS{}
+	mps3.On("CPUTimes").Return([]cpu.TimesStat{cts3}, nil)
+	cs.ps = &mps3
+
+	err = cs.Gather(&acc)
+	require.NoError(t, err)
+
+	assertContainsTaggedFloat(t, &acc, "cpu", "time_user", 56, 0, cputags)
+	assertContainsTaggedFloat(t, &acc, "cpu", "time_idle", 120, 0, cputags)
+	assertContainsTaggedFloat(t, &acc, "cpu", "time_iowait", 3, 0, cputags)
+
+	assertContainsTaggedFloat(t, &acc, "cpu", "usage_user", 18, 0.0005, cputags)
+	assertContainsTaggedFloat(t, &acc, "cpu", "usage_idle", 80, 0.0005, cputags)
+	assertContainsTaggedFloat(t, &acc, "cpu", "usage_iowait", 2, 0.0005, cputags)
+}