diff --git a/metrics/counter.go b/metrics/counter.go
index 05ec419585..cb81599c21 100644
--- a/metrics/counter.go
+++ b/metrics/counter.go
@@ -82,7 +82,6 @@ func (c counterSnapshot) Count() int64 { return int64(c) }
 // NilCounter is a no-op Counter.
 type NilCounter struct{}
 
-// Clear is a no-op.
 func (NilCounter) Clear()                    {}
 func (NilCounter) Dec(i int64)               {}
 func (NilCounter) Inc(i int64)               {}
diff --git a/metrics/ewma.go b/metrics/ewma.go
index e695c48d82..1d7a4f00cf 100644
--- a/metrics/ewma.go
+++ b/metrics/ewma.go
@@ -39,12 +39,12 @@ func NewEWMA15() EWMA {
 	return NewEWMA(1 - math.Exp(-5.0/60.0/15))
 }
 
-// eWMASnapshot is a read-only copy of another EWMA.
-type eWMASnapshot float64
+// ewmaSnapshot is a read-only copy of another EWMA.
+type ewmaSnapshot float64
 
 // Rate returns the rate of events per second at the time the snapshot was
 // taken.
-func (a eWMASnapshot) Rate() float64 { return float64(a) }
+func (a ewmaSnapshot) Rate() float64 { return float64(a) }
 
 // NilEWMA is a no-op EWMA.
 type NilEWMA struct{}
@@ -67,7 +67,7 @@ type StandardEWMA struct {
 // Snapshot returns a read-only copy of the EWMA.
 func (a *StandardEWMA) Snapshot() EWMASnapshot {
 	r := math.Float64frombits(a.rate.Load()) * float64(time.Second)
-	return eWMASnapshot(r)
+	return ewmaSnapshot(r)
 }
 
 // Tick ticks the clock to update the moving average.  It assumes it is called
diff --git a/metrics/gauge.go b/metrics/gauge.go
index d1a56bbdda..68f8f11abc 100644
--- a/metrics/gauge.go
+++ b/metrics/gauge.go
@@ -76,8 +76,14 @@ func (g *StandardGauge) Update(v int64) {
 
 // Update updates the gauge's value if v is larger then the current valie.
 func (g *StandardGauge) UpdateIfGt(v int64) {
-	if g.value.Load() < v {
-		g.value.Store(v)
+	for {
+		exist := g.value.Load()
+		if exist >= v {
+			break
+		}
+		if g.value.CompareAndSwap(exist, v) {
+			break
+		}
 	}
 }
 
diff --git a/metrics/gauge_float64.go b/metrics/gauge_float64.go
index 2f509b1cec..967f2bc60e 100644
--- a/metrics/gauge_float64.go
+++ b/metrics/gauge_float64.go
@@ -51,14 +51,9 @@ func (g gaugeFloat64Snapshot) Value() float64 { return float64(g) }
 // NilGauge is a no-op Gauge.
 type NilGaugeFloat64 struct{}
 
-// Snapshot is a no-op.
 func (NilGaugeFloat64) Snapshot() GaugeFloat64Snapshot { return NilGaugeFloat64{} }
-
-// Update is a no-op.
-func (NilGaugeFloat64) Update(v float64) {}
-
-// Value is a no-op.
-func (NilGaugeFloat64) Value() float64 { return 0.0 }
+func (NilGaugeFloat64) Update(v float64)               {}
+func (NilGaugeFloat64) Value() float64                 { return 0.0 }
 
 // StandardGaugeFloat64 is the standard implementation of a GaugeFloat64 and uses
 // atomic to manage a single float64 value.
diff --git a/metrics/sample.go b/metrics/sample.go
index 96598aec71..d204024f6b 100644
--- a/metrics/sample.go
+++ b/metrics/sample.go
@@ -148,7 +148,7 @@ func (NilSample) Clear()                   {}
 func (NilSample) Snapshot() SampleSnapshot { return (*emptySnapshot)(nil) }
 func (NilSample) Update(v int64)           {}
 
-// CalculatePercentiles returns an arbitrary percentile of the slice of int64.
+// SamplePercentiles returns an arbitrary percentile of the slice of int64.
 func SamplePercentile(values []int64, p float64) float64 {
 	return CalculatePercentiles(values, []float64{p})[0]
 }