1 files changed, 186 insertions, 0 deletions
diff --git a/pkg/sentry/time/calibrated_clock_test.go b/pkg/sentry/time/calibrated_clock_test.go
new file mode 100644
index 000000000..8b6dd5592
--- /dev/null
+++ b/pkg/sentry/time/calibrated_clock_test.go
@@ -0,0 +1,186 @@
+// Copyright 2018 Google Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package time
+
+import (
+	"testing"
+	"time"
+)
+
+// newTestCalibratedClock returns a CalibratedClock that collects samples from
+// the given sample list and cycle counts from the given cycle list.
+func newTestCalibratedClock(samples []sample, cycles []TSCValue) *CalibratedClock {
+	return &CalibratedClock{
+		ref: newTestSampler(samples, cycles),
+	}
+}
+
+func TestConstantFrequency(t *testing.T) {
+	// Perfectly constant frequency.
+	samples := []sample{
+		{before: 100000, after: 100000 + defaultOverheadCycles, ref: 100},
+		{before: 200000, after: 200000 + defaultOverheadCycles, ref: 200},
+		{before: 300000, after: 300000 + defaultOverheadCycles, ref: 300},
+		{before: 400000, after: 400000 + defaultOverheadCycles, ref: 400},
+		{before: 500000, after: 500000 + defaultOverheadCycles, ref: 500},
+		{before: 600000, after: 600000 + defaultOverheadCycles, ref: 600},
+		{before: 700000, after: 700000 + defaultOverheadCycles, ref: 700},
+	}
+
+	c := newTestCalibratedClock(samples, nil)
+
+	// Update from all samples.
+	for range samples {
+		c.Update()
+	}
+
+	c.mu.RLock()
+	if !c.ready {
+		c.mu.RUnlock()
+		t.Fatalf("clock not ready")
+	}
+	// A bit after the last sample.
+	now, ok := c.params.ComputeTime(750000)
+	c.mu.RUnlock()
+	if !ok {
+		t.Fatalf("ComputeTime ok got %v want true", ok)
+	}
+
+	t.Logf("now: %v", now)
+
+	// Time should be between the current sample and where we'd expect the
+	// next sample.
+	if now < 700 || now > 800 {
+		t.Errorf("now got %v want > 700 && < 800", now)
+	}
+}
+
+func TestErrorCorrection(t *testing.T) {
+	testCases := []struct {
+		name               string
+		samples            [5]sample
+		projectedTimeStart int64
+		projectedTimeEnd   int64
+	}{
+		// Initial calibration should be ~1MHz for each of these, and
+		// the reference clock changes in samples[2].
+		{
+			name: "slow-down",
+			samples: [5]sample{
+				{before: 1000000, after: 1000001, ref: ReferenceNS(1 * ApproxUpdateInterval.Nanoseconds())},
+				{before: 2000000, after: 2000001, ref: ReferenceNS(2 * ApproxUpdateInterval.Nanoseconds())},
+				// Reference clock has slowed down, causing 100ms of error.
+				{before: 3010000, after: 3010001, ref: ReferenceNS(3 * ApproxUpdateInterval.Nanoseconds())},
+				{before: 4020000, after: 4020001, ref: ReferenceNS(4 * ApproxUpdateInterval.Nanoseconds())},
+				{before: 5030000, after: 5030001, ref: ReferenceNS(5 * ApproxUpdateInterval.Nanoseconds())},
+			},
+			projectedTimeStart: 3005 * time.Millisecond.Nanoseconds(),
+			projectedTimeEnd:   3015 * time.Millisecond.Nanoseconds(),
+		},
+		{
+			name: "speed-up",
+			samples: [5]sample{
+				{before: 1000000, after: 1000001, ref: ReferenceNS(1 * ApproxUpdateInterval.Nanoseconds())},
+				{before: 2000000, after: 2000001, ref: ReferenceNS(2 * ApproxUpdateInterval.Nanoseconds())},
+				// Reference clock has sped up, causing 100ms of error.
+				{before: 2990000, after: 2990001, ref: ReferenceNS(3 * ApproxUpdateInterval.Nanoseconds())},
+				{before: 3980000, after: 3980001, ref: ReferenceNS(4 * ApproxUpdateInterval.Nanoseconds())},
+				{before: 4970000, after: 4970001, ref: ReferenceNS(5 * ApproxUpdateInterval.Nanoseconds())},
+			},
+			projectedTimeStart: 2985 * time.Millisecond.Nanoseconds(),
+			projectedTimeEnd:   2995 * time.Millisecond.Nanoseconds(),
+		},
+	}
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			c := newTestCalibratedClock(tc.samples[:], nil)
+
+			// Initial calibration takes two updates.
+			_, ok := c.Update()
+			if ok {
+				t.Fatalf("Update ready too early")
+			}
+
+			params, ok := c.Update()
+			if !ok {
+				t.Fatalf("Update not ready")
+			}
+
+			// Initial calibration is ~1MHz.
+			hz := params.Frequency
+			if hz < 990000 || hz > 1010000 {
+				t.Fatalf("Frequency got %v want > 990kHz && < 1010kHz", hz)
+			}
+
+			// Project time at the next update. Given the 1MHz
+			// calibration, it is expected to be ~3.1s/2.9s, not
+			// the actual 3s.
+			//
+			// N.B. the next update time is the "after" time above.
+			projected, ok := params.ComputeTime(tc.samples[2].after)
+			if !ok {
+				t.Fatalf("ComputeTime ok got %v want true", ok)
+			}
+			if projected < tc.projectedTimeStart || projected > tc.projectedTimeEnd {
+				t.Fatalf("ComputeTime(%v) got %v want > %v && < %v", tc.samples[2].after, projected, tc.projectedTimeStart, tc.projectedTimeEnd)
+			}
+
+			// Update again to see the changed reference clock.
+			params, ok = c.Update()
+			if !ok {
+				t.Fatalf("Update not ready")
+			}
+
+			// We now know that TSC = tc.samples[2].after -> 3s,
+			// but with the previous params indicated that TSC
+			// tc.samples[2].after -> 3.5s/2.5s. We can't allow the
+			// clock to go backwards, and having the clock jump
+			// forwards is undesirable. There should be a smooth
+			// transition that corrects the clock error over time.
+			// Check that the clock is continuous at TSC =
+			// tc.samples[2].after.
+			newProjected, ok := params.ComputeTime(tc.samples[2].after)
+			if !ok {
+				t.Fatalf("ComputeTime ok got %v want true", ok)
+			}
+			if newProjected != projected {
+				t.Errorf("Discontinuous time; ComputeTime(%v) got %v want %v", tc.samples[2].after, newProjected, projected)
+			}
+
+			// As the reference clock stablizes, ensure that the clock error
+			// decreases.
+			initialErr := c.errorNS
+			t.Logf("initial error: %v ns", initialErr)
+
+			_, ok = c.Update()
+			if !ok {
+				t.Fatalf("Update not ready")
+			}
+			if c.errorNS.Magnitude() > initialErr.Magnitude() {
+				t.Errorf("errorNS increased, got %v want |%v| <= |%v|", c.errorNS, c.errorNS, initialErr)
+			}
+
+			_, ok = c.Update()
+			if !ok {
+				t.Fatalf("Update not ready")
+			}
+			if c.errorNS.Magnitude() > initialErr.Magnitude() {
+				t.Errorf("errorNS increased, got %v want |%v| <= |%v|", c.errorNS, c.errorNS, initialErr)
+			}
+
+			t.Logf("final error: %v ns", c.errorNS)
+		})
+	}
+}