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-rw-r--r--src/runtime/mgcpacer_test.go1097
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diff --git a/src/runtime/mgcpacer_test.go b/src/runtime/mgcpacer_test.go
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+++ b/src/runtime/mgcpacer_test.go
@@ -0,0 +1,1097 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package runtime_test
+
+import (
+ "fmt"
+ "math"
+ "math/rand"
+ . "runtime"
+ "testing"
+ "time"
+)
+
+func TestGcPacer(t *testing.T) {
+ t.Parallel()
+
+ const initialHeapBytes = 256 << 10
+ for _, e := range []*gcExecTest{
+ {
+ // The most basic test case: a steady-state heap.
+ // Growth to an O(MiB) heap, then constant heap size, alloc/scan rates.
+ name: "Steady",
+ gcPercent: 100,
+ memoryLimit: math.MaxInt64,
+ globalsBytes: 32 << 10,
+ nCores: 8,
+ allocRate: constant(33.0),
+ scanRate: constant(1024.0),
+ growthRate: constant(2.0).sum(ramp(-1.0, 12)),
+ scannableFrac: constant(1.0),
+ stackBytes: constant(8192),
+ length: 50,
+ checker: func(t *testing.T, c []gcCycleResult) {
+ n := len(c)
+ if n >= 25 {
+ // At this alloc/scan rate, the pacer should be extremely close to the goal utilization.
+ assertInEpsilon(t, "GC utilization", c[n-1].gcUtilization, GCGoalUtilization, 0.005)
+
+ // Make sure the pacer settles into a non-degenerate state in at least 25 GC cycles.
+ assertInEpsilon(t, "GC utilization", c[n-1].gcUtilization, c[n-2].gcUtilization, 0.005)
+ assertInRange(t, "goal ratio", c[n-1].goalRatio(), 0.95, 1.05)
+ }
+ },
+ },
+ {
+ // Same as the steady-state case, but lots of stacks to scan relative to the heap size.
+ name: "SteadyBigStacks",
+ gcPercent: 100,
+ memoryLimit: math.MaxInt64,
+ globalsBytes: 32 << 10,
+ nCores: 8,
+ allocRate: constant(132.0),
+ scanRate: constant(1024.0),
+ growthRate: constant(2.0).sum(ramp(-1.0, 12)),
+ scannableFrac: constant(1.0),
+ stackBytes: constant(2048).sum(ramp(128<<20, 8)),
+ length: 50,
+ checker: func(t *testing.T, c []gcCycleResult) {
+ // Check the same conditions as the steady-state case, except the old pacer can't
+ // really handle this well, so don't check the goal ratio for it.
+ n := len(c)
+ if n >= 25 {
+ // For the pacer redesign, assert something even stronger: at this alloc/scan rate,
+ // it should be extremely close to the goal utilization.
+ assertInEpsilon(t, "GC utilization", c[n-1].gcUtilization, GCGoalUtilization, 0.005)
+ assertInRange(t, "goal ratio", c[n-1].goalRatio(), 0.95, 1.05)
+
+ // Make sure the pacer settles into a non-degenerate state in at least 25 GC cycles.
+ assertInEpsilon(t, "GC utilization", c[n-1].gcUtilization, c[n-2].gcUtilization, 0.005)
+ }
+ },
+ },
+ {
+ // Same as the steady-state case, but lots of globals to scan relative to the heap size.
+ name: "SteadyBigGlobals",
+ gcPercent: 100,
+ memoryLimit: math.MaxInt64,
+ globalsBytes: 128 << 20,
+ nCores: 8,
+ allocRate: constant(132.0),
+ scanRate: constant(1024.0),
+ growthRate: constant(2.0).sum(ramp(-1.0, 12)),
+ scannableFrac: constant(1.0),
+ stackBytes: constant(8192),
+ length: 50,
+ checker: func(t *testing.T, c []gcCycleResult) {
+ // Check the same conditions as the steady-state case, except the old pacer can't
+ // really handle this well, so don't check the goal ratio for it.
+ n := len(c)
+ if n >= 25 {
+ // For the pacer redesign, assert something even stronger: at this alloc/scan rate,
+ // it should be extremely close to the goal utilization.
+ assertInEpsilon(t, "GC utilization", c[n-1].gcUtilization, GCGoalUtilization, 0.005)
+ assertInRange(t, "goal ratio", c[n-1].goalRatio(), 0.95, 1.05)
+
+ // Make sure the pacer settles into a non-degenerate state in at least 25 GC cycles.
+ assertInEpsilon(t, "GC utilization", c[n-1].gcUtilization, c[n-2].gcUtilization, 0.005)
+ }
+ },
+ },
+ {
+ // This tests the GC pacer's response to a small change in allocation rate.
+ name: "StepAlloc",
+ gcPercent: 100,
+ memoryLimit: math.MaxInt64,
+ globalsBytes: 32 << 10,
+ nCores: 8,
+ allocRate: constant(33.0).sum(ramp(66.0, 1).delay(50)),
+ scanRate: constant(1024.0),
+ growthRate: constant(2.0).sum(ramp(-1.0, 12)),
+ scannableFrac: constant(1.0),
+ stackBytes: constant(8192),
+ length: 100,
+ checker: func(t *testing.T, c []gcCycleResult) {
+ n := len(c)
+ if (n >= 25 && n < 50) || n >= 75 {
+ // Make sure the pacer settles into a non-degenerate state in at least 25 GC cycles
+ // and then is able to settle again after a significant jump in allocation rate.
+ assertInEpsilon(t, "GC utilization", c[n-1].gcUtilization, c[n-2].gcUtilization, 0.005)
+ assertInRange(t, "goal ratio", c[n-1].goalRatio(), 0.95, 1.05)
+ }
+ },
+ },
+ {
+ // This tests the GC pacer's response to a large change in allocation rate.
+ name: "HeavyStepAlloc",
+ gcPercent: 100,
+ memoryLimit: math.MaxInt64,
+ globalsBytes: 32 << 10,
+ nCores: 8,
+ allocRate: constant(33).sum(ramp(330, 1).delay(50)),
+ scanRate: constant(1024.0),
+ growthRate: constant(2.0).sum(ramp(-1.0, 12)),
+ scannableFrac: constant(1.0),
+ stackBytes: constant(8192),
+ length: 100,
+ checker: func(t *testing.T, c []gcCycleResult) {
+ n := len(c)
+ if (n >= 25 && n < 50) || n >= 75 {
+ // Make sure the pacer settles into a non-degenerate state in at least 25 GC cycles
+ // and then is able to settle again after a significant jump in allocation rate.
+ assertInEpsilon(t, "GC utilization", c[n-1].gcUtilization, c[n-2].gcUtilization, 0.005)
+ assertInRange(t, "goal ratio", c[n-1].goalRatio(), 0.95, 1.05)
+ }
+ },
+ },
+ {
+ // This tests the GC pacer's response to a change in the fraction of the scannable heap.
+ name: "StepScannableFrac",
+ gcPercent: 100,
+ memoryLimit: math.MaxInt64,
+ globalsBytes: 32 << 10,
+ nCores: 8,
+ allocRate: constant(128.0),
+ scanRate: constant(1024.0),
+ growthRate: constant(2.0).sum(ramp(-1.0, 12)),
+ scannableFrac: constant(0.2).sum(unit(0.5).delay(50)),
+ stackBytes: constant(8192),
+ length: 100,
+ checker: func(t *testing.T, c []gcCycleResult) {
+ n := len(c)
+ if (n >= 25 && n < 50) || n >= 75 {
+ // Make sure the pacer settles into a non-degenerate state in at least 25 GC cycles
+ // and then is able to settle again after a significant jump in allocation rate.
+ assertInEpsilon(t, "GC utilization", c[n-1].gcUtilization, c[n-2].gcUtilization, 0.005)
+ assertInRange(t, "goal ratio", c[n-1].goalRatio(), 0.95, 1.05)
+ }
+ },
+ },
+ {
+ // Tests the pacer for a high GOGC value with a large heap growth happening
+ // in the middle. The purpose of the large heap growth is to check if GC
+ // utilization ends up sensitive
+ name: "HighGOGC",
+ gcPercent: 1500,
+ memoryLimit: math.MaxInt64,
+ globalsBytes: 32 << 10,
+ nCores: 8,
+ allocRate: random(7, 0x53).offset(165),
+ scanRate: constant(1024.0),
+ growthRate: constant(2.0).sum(ramp(-1.0, 12), random(0.01, 0x1), unit(14).delay(25)),
+ scannableFrac: constant(1.0),
+ stackBytes: constant(8192),
+ length: 50,
+ checker: func(t *testing.T, c []gcCycleResult) {
+ n := len(c)
+ if n > 12 {
+ if n == 26 {
+ // In the 26th cycle there's a heap growth. Overshoot is expected to maintain
+ // a stable utilization, but we should *never* overshoot more than GOGC of
+ // the next cycle.
+ assertInRange(t, "goal ratio", c[n-1].goalRatio(), 0.90, 15)
+ } else {
+ // Give a wider goal range here. With such a high GOGC value we're going to be
+ // forced to undershoot.
+ //
+ // TODO(mknyszek): Instead of placing a 0.95 limit on the trigger, make the limit
+ // based on absolute bytes, that's based somewhat in how the minimum heap size
+ // is determined.
+ assertInRange(t, "goal ratio", c[n-1].goalRatio(), 0.90, 1.05)
+ }
+
+ // Ensure utilization remains stable despite a growth in live heap size
+ // at GC #25. This test fails prior to the GC pacer redesign.
+ //
+ // Because GOGC is so large, we should also be really close to the goal utilization.
+ assertInEpsilon(t, "GC utilization", c[n-1].gcUtilization, GCGoalUtilization, GCGoalUtilization+0.03)
+ assertInEpsilon(t, "GC utilization", c[n-1].gcUtilization, c[n-2].gcUtilization, 0.03)
+ }
+ },
+ },
+ {
+ // This test makes sure that in the face of a varying (in this case, oscillating) allocation
+ // rate, the pacer does a reasonably good job of staying abreast of the changes.
+ name: "OscAlloc",
+ gcPercent: 100,
+ memoryLimit: math.MaxInt64,
+ globalsBytes: 32 << 10,
+ nCores: 8,
+ allocRate: oscillate(13, 0, 8).offset(67),
+ scanRate: constant(1024.0),
+ growthRate: constant(2.0).sum(ramp(-1.0, 12)),
+ scannableFrac: constant(1.0),
+ stackBytes: constant(8192),
+ length: 50,
+ checker: func(t *testing.T, c []gcCycleResult) {
+ n := len(c)
+ if n > 12 {
+ // After the 12th GC, the heap will stop growing. Now, just make sure that:
+ // 1. Utilization isn't varying _too_ much, and
+ // 2. The pacer is mostly keeping up with the goal.
+ assertInRange(t, "goal ratio", c[n-1].goalRatio(), 0.95, 1.05)
+ assertInRange(t, "GC utilization", c[n-1].gcUtilization, 0.25, 0.3)
+ }
+ },
+ },
+ {
+ // This test is the same as OscAlloc, but instead of oscillating, the allocation rate is jittery.
+ name: "JitterAlloc",
+ gcPercent: 100,
+ memoryLimit: math.MaxInt64,
+ globalsBytes: 32 << 10,
+ nCores: 8,
+ allocRate: random(13, 0xf).offset(132),
+ scanRate: constant(1024.0),
+ growthRate: constant(2.0).sum(ramp(-1.0, 12), random(0.01, 0xe)),
+ scannableFrac: constant(1.0),
+ stackBytes: constant(8192),
+ length: 50,
+ checker: func(t *testing.T, c []gcCycleResult) {
+ n := len(c)
+ if n > 12 {
+ // After the 12th GC, the heap will stop growing. Now, just make sure that:
+ // 1. Utilization isn't varying _too_ much, and
+ // 2. The pacer is mostly keeping up with the goal.
+ assertInRange(t, "goal ratio", c[n-1].goalRatio(), 0.95, 1.025)
+ assertInRange(t, "GC utilization", c[n-1].gcUtilization, 0.25, 0.275)
+ }
+ },
+ },
+ {
+ // This test is the same as JitterAlloc, but with a much higher allocation rate.
+ // The jitter is proportionally the same.
+ name: "HeavyJitterAlloc",
+ gcPercent: 100,
+ memoryLimit: math.MaxInt64,
+ globalsBytes: 32 << 10,
+ nCores: 8,
+ allocRate: random(33.0, 0x0).offset(330),
+ scanRate: constant(1024.0),
+ growthRate: constant(2.0).sum(ramp(-1.0, 12), random(0.01, 0x152)),
+ scannableFrac: constant(1.0),
+ stackBytes: constant(8192),
+ length: 50,
+ checker: func(t *testing.T, c []gcCycleResult) {
+ n := len(c)
+ if n > 13 {
+ // After the 12th GC, the heap will stop growing. Now, just make sure that:
+ // 1. Utilization isn't varying _too_ much, and
+ // 2. The pacer is mostly keeping up with the goal.
+ // We start at the 13th here because we want to use the 12th as a reference.
+ assertInRange(t, "goal ratio", c[n-1].goalRatio(), 0.95, 1.05)
+ // Unlike the other tests, GC utilization here will vary more and tend higher.
+ // Just make sure it's not going too crazy.
+ assertInEpsilon(t, "GC utilization", c[n-1].gcUtilization, c[n-2].gcUtilization, 0.05)
+ assertInEpsilon(t, "GC utilization", c[n-1].gcUtilization, c[11].gcUtilization, 0.05)
+ }
+ },
+ },
+ {
+ // This test sets a slow allocation rate and a small heap (close to the minimum heap size)
+ // to try to minimize the difference between the trigger and the goal.
+ name: "SmallHeapSlowAlloc",
+ gcPercent: 100,
+ memoryLimit: math.MaxInt64,
+ globalsBytes: 32 << 10,
+ nCores: 8,
+ allocRate: constant(1.0),
+ scanRate: constant(2048.0),
+ growthRate: constant(2.0).sum(ramp(-1.0, 3)),
+ scannableFrac: constant(0.01),
+ stackBytes: constant(8192),
+ length: 50,
+ checker: func(t *testing.T, c []gcCycleResult) {
+ n := len(c)
+ if n > 4 {
+ // After the 4th GC, the heap will stop growing.
+ // First, let's make sure we're finishing near the goal, with some extra
+ // room because we're probably going to be triggering early.
+ assertInRange(t, "goal ratio", c[n-1].goalRatio(), 0.925, 1.025)
+ // Next, let's make sure there's some minimum distance between the goal
+ // and the trigger. It should be proportional to the runway (hence the
+ // trigger ratio check, instead of a check against the runway).
+ assertInRange(t, "trigger ratio", c[n-1].triggerRatio(), 0.925, 0.975)
+ }
+ if n > 25 {
+ // Double-check that GC utilization looks OK.
+
+ // At this alloc/scan rate, the pacer should be extremely close to the goal utilization.
+ assertInEpsilon(t, "GC utilization", c[n-1].gcUtilization, GCGoalUtilization, 0.005)
+ // Make sure GC utilization has mostly levelled off.
+ assertInEpsilon(t, "GC utilization", c[n-1].gcUtilization, c[n-2].gcUtilization, 0.05)
+ assertInEpsilon(t, "GC utilization", c[n-1].gcUtilization, c[11].gcUtilization, 0.05)
+ }
+ },
+ },
+ {
+ // This test sets a slow allocation rate and a medium heap (around 10x the min heap size)
+ // to try to minimize the difference between the trigger and the goal.
+ name: "MediumHeapSlowAlloc",
+ gcPercent: 100,
+ memoryLimit: math.MaxInt64,
+ globalsBytes: 32 << 10,
+ nCores: 8,
+ allocRate: constant(1.0),
+ scanRate: constant(2048.0),
+ growthRate: constant(2.0).sum(ramp(-1.0, 8)),
+ scannableFrac: constant(0.01),
+ stackBytes: constant(8192),
+ length: 50,
+ checker: func(t *testing.T, c []gcCycleResult) {
+ n := len(c)
+ if n > 9 {
+ // After the 4th GC, the heap will stop growing.
+ // First, let's make sure we're finishing near the goal, with some extra
+ // room because we're probably going to be triggering early.
+ assertInRange(t, "goal ratio", c[n-1].goalRatio(), 0.925, 1.025)
+ // Next, let's make sure there's some minimum distance between the goal
+ // and the trigger. It should be proportional to the runway (hence the
+ // trigger ratio check, instead of a check against the runway).
+ assertInRange(t, "trigger ratio", c[n-1].triggerRatio(), 0.925, 0.975)
+ }
+ if n > 25 {
+ // Double-check that GC utilization looks OK.
+
+ // At this alloc/scan rate, the pacer should be extremely close to the goal utilization.
+ assertInEpsilon(t, "GC utilization", c[n-1].gcUtilization, GCGoalUtilization, 0.005)
+ // Make sure GC utilization has mostly levelled off.
+ assertInEpsilon(t, "GC utilization", c[n-1].gcUtilization, c[n-2].gcUtilization, 0.05)
+ assertInEpsilon(t, "GC utilization", c[n-1].gcUtilization, c[11].gcUtilization, 0.05)
+ }
+ },
+ },
+ {
+ // This test sets a slow allocation rate and a large heap to try to minimize the
+ // difference between the trigger and the goal.
+ name: "LargeHeapSlowAlloc",
+ gcPercent: 100,
+ memoryLimit: math.MaxInt64,
+ globalsBytes: 32 << 10,
+ nCores: 8,
+ allocRate: constant(1.0),
+ scanRate: constant(2048.0),
+ growthRate: constant(4.0).sum(ramp(-3.0, 12)),
+ scannableFrac: constant(0.01),
+ stackBytes: constant(8192),
+ length: 50,
+ checker: func(t *testing.T, c []gcCycleResult) {
+ n := len(c)
+ if n > 13 {
+ // After the 4th GC, the heap will stop growing.
+ // First, let's make sure we're finishing near the goal.
+ assertInRange(t, "goal ratio", c[n-1].goalRatio(), 0.95, 1.05)
+ // Next, let's make sure there's some minimum distance between the goal
+ // and the trigger. It should be around the default minimum heap size.
+ assertInRange(t, "runway", c[n-1].runway(), DefaultHeapMinimum-64<<10, DefaultHeapMinimum+64<<10)
+ }
+ if n > 25 {
+ // Double-check that GC utilization looks OK.
+
+ // At this alloc/scan rate, the pacer should be extremely close to the goal utilization.
+ assertInEpsilon(t, "GC utilization", c[n-1].gcUtilization, GCGoalUtilization, 0.005)
+ // Make sure GC utilization has mostly levelled off.
+ assertInEpsilon(t, "GC utilization", c[n-1].gcUtilization, c[n-2].gcUtilization, 0.05)
+ assertInEpsilon(t, "GC utilization", c[n-1].gcUtilization, c[11].gcUtilization, 0.05)
+ }
+ },
+ },
+ {
+ // The most basic test case with a memory limit: a steady-state heap.
+ // Growth to an O(MiB) heap, then constant heap size, alloc/scan rates.
+ // Provide a lot of room for the limit. Essentially, this should behave just like
+ // the "Steady" test. Note that we don't simulate non-heap overheads, so the
+ // memory limit and the heap limit are identical.
+ name: "SteadyMemoryLimit",
+ gcPercent: 100,
+ memoryLimit: 512 << 20,
+ globalsBytes: 32 << 10,
+ nCores: 8,
+ allocRate: constant(33.0),
+ scanRate: constant(1024.0),
+ growthRate: constant(2.0).sum(ramp(-1.0, 12)),
+ scannableFrac: constant(1.0),
+ stackBytes: constant(8192),
+ length: 50,
+ checker: func(t *testing.T, c []gcCycleResult) {
+ n := len(c)
+ if peak := c[n-1].heapPeak; peak >= applyMemoryLimitHeapGoalHeadroom(512<<20) {
+ t.Errorf("peak heap size reaches heap limit: %d", peak)
+ }
+ if n >= 25 {
+ // At this alloc/scan rate, the pacer should be extremely close to the goal utilization.
+ assertInEpsilon(t, "GC utilization", c[n-1].gcUtilization, GCGoalUtilization, 0.005)
+
+ // Make sure the pacer settles into a non-degenerate state in at least 25 GC cycles.
+ assertInEpsilon(t, "GC utilization", c[n-1].gcUtilization, c[n-2].gcUtilization, 0.005)
+ assertInRange(t, "goal ratio", c[n-1].goalRatio(), 0.95, 1.05)
+ }
+ },
+ },
+ {
+ // This is the same as the previous test, but gcPercent = -1, so the heap *should* grow
+ // all the way to the peak.
+ name: "SteadyMemoryLimitNoGCPercent",
+ gcPercent: -1,
+ memoryLimit: 512 << 20,
+ globalsBytes: 32 << 10,
+ nCores: 8,
+ allocRate: constant(33.0),
+ scanRate: constant(1024.0),
+ growthRate: constant(2.0).sum(ramp(-1.0, 12)),
+ scannableFrac: constant(1.0),
+ stackBytes: constant(8192),
+ length: 50,
+ checker: func(t *testing.T, c []gcCycleResult) {
+ n := len(c)
+ if goal := c[n-1].heapGoal; goal != applyMemoryLimitHeapGoalHeadroom(512<<20) {
+ t.Errorf("heap goal is not the heap limit: %d", goal)
+ }
+ if n >= 25 {
+ // At this alloc/scan rate, the pacer should be extremely close to the goal utilization.
+ assertInEpsilon(t, "GC utilization", c[n-1].gcUtilization, GCGoalUtilization, 0.005)
+
+ // Make sure the pacer settles into a non-degenerate state in at least 25 GC cycles.
+ assertInEpsilon(t, "GC utilization", c[n-1].gcUtilization, c[n-2].gcUtilization, 0.005)
+ assertInRange(t, "goal ratio", c[n-1].goalRatio(), 0.95, 1.05)
+ }
+ },
+ },
+ {
+ // This test ensures that the pacer doesn't fall over even when the live heap exceeds
+ // the memory limit. It also makes sure GC utilization actually rises to push back.
+ name: "ExceedMemoryLimit",
+ gcPercent: 100,
+ memoryLimit: 512 << 20,
+ globalsBytes: 32 << 10,
+ nCores: 8,
+ allocRate: constant(33.0),
+ scanRate: constant(1024.0),
+ growthRate: constant(3.5).sum(ramp(-2.5, 12)),
+ scannableFrac: constant(1.0),
+ stackBytes: constant(8192),
+ length: 50,
+ checker: func(t *testing.T, c []gcCycleResult) {
+ n := len(c)
+ if n > 12 {
+ // We're way over the memory limit, so we want to make sure our goal is set
+ // as low as it possibly can be.
+ if goal, live := c[n-1].heapGoal, c[n-1].heapLive; goal != live {
+ t.Errorf("heap goal is not equal to live heap: %d != %d", goal, live)
+ }
+ }
+ if n >= 25 {
+ // Due to memory pressure, we should scale to 100% GC CPU utilization.
+ // Note that in practice this won't actually happen because of the CPU limiter,
+ // but it's not the pacer's job to limit CPU usage.
+ assertInEpsilon(t, "GC utilization", c[n-1].gcUtilization, 1.0, 0.005)
+
+ // Make sure the pacer settles into a non-degenerate state in at least 25 GC cycles.
+ // In this case, that just means it's not wavering around a whole bunch.
+ assertInEpsilon(t, "GC utilization", c[n-1].gcUtilization, c[n-2].gcUtilization, 0.005)
+ }
+ },
+ },
+ {
+ // Same as the previous test, but with gcPercent = -1.
+ name: "ExceedMemoryLimitNoGCPercent",
+ gcPercent: -1,
+ memoryLimit: 512 << 20,
+ globalsBytes: 32 << 10,
+ nCores: 8,
+ allocRate: constant(33.0),
+ scanRate: constant(1024.0),
+ growthRate: constant(3.5).sum(ramp(-2.5, 12)),
+ scannableFrac: constant(1.0),
+ stackBytes: constant(8192),
+ length: 50,
+ checker: func(t *testing.T, c []gcCycleResult) {
+ n := len(c)
+ if n < 10 {
+ if goal := c[n-1].heapGoal; goal != applyMemoryLimitHeapGoalHeadroom(512<<20) {
+ t.Errorf("heap goal is not the heap limit: %d", goal)
+ }
+ }
+ if n > 12 {
+ // We're way over the memory limit, so we want to make sure our goal is set
+ // as low as it possibly can be.
+ if goal, live := c[n-1].heapGoal, c[n-1].heapLive; goal != live {
+ t.Errorf("heap goal is not equal to live heap: %d != %d", goal, live)
+ }
+ }
+ if n >= 25 {
+ // Due to memory pressure, we should scale to 100% GC CPU utilization.
+ // Note that in practice this won't actually happen because of the CPU limiter,
+ // but it's not the pacer's job to limit CPU usage.
+ assertInEpsilon(t, "GC utilization", c[n-1].gcUtilization, 1.0, 0.005)
+
+ // Make sure the pacer settles into a non-degenerate state in at least 25 GC cycles.
+ // In this case, that just means it's not wavering around a whole bunch.
+ assertInEpsilon(t, "GC utilization", c[n-1].gcUtilization, c[n-2].gcUtilization, 0.005)
+ }
+ },
+ },
+ {
+ // This test ensures that the pacer maintains the memory limit as the heap grows.
+ name: "MaintainMemoryLimit",
+ gcPercent: 100,
+ memoryLimit: 512 << 20,
+ globalsBytes: 32 << 10,
+ nCores: 8,
+ allocRate: constant(33.0),
+ scanRate: constant(1024.0),
+ growthRate: constant(3.0).sum(ramp(-2.0, 12)),
+ scannableFrac: constant(1.0),
+ stackBytes: constant(8192),
+ length: 50,
+ checker: func(t *testing.T, c []gcCycleResult) {
+ n := len(c)
+ if n > 12 {
+ // We're trying to saturate the memory limit.
+ if goal := c[n-1].heapGoal; goal != applyMemoryLimitHeapGoalHeadroom(512<<20) {
+ t.Errorf("heap goal is not the heap limit: %d", goal)
+ }
+ }
+ if n >= 25 {
+ // At this alloc/scan rate, the pacer should be extremely close to the goal utilization,
+ // even with the additional memory pressure.
+ assertInEpsilon(t, "GC utilization", c[n-1].gcUtilization, GCGoalUtilization, 0.005)
+
+ // Make sure the pacer settles into a non-degenerate state in at least 25 GC cycles and
+ // that it's meeting its goal.
+ assertInEpsilon(t, "GC utilization", c[n-1].gcUtilization, c[n-2].gcUtilization, 0.005)
+ assertInRange(t, "goal ratio", c[n-1].goalRatio(), 0.95, 1.05)
+ }
+ },
+ },
+ {
+ // Same as the previous test, but with gcPercent = -1.
+ name: "MaintainMemoryLimitNoGCPercent",
+ gcPercent: -1,
+ memoryLimit: 512 << 20,
+ globalsBytes: 32 << 10,
+ nCores: 8,
+ allocRate: constant(33.0),
+ scanRate: constant(1024.0),
+ growthRate: constant(3.0).sum(ramp(-2.0, 12)),
+ scannableFrac: constant(1.0),
+ stackBytes: constant(8192),
+ length: 50,
+ checker: func(t *testing.T, c []gcCycleResult) {
+ n := len(c)
+ if goal := c[n-1].heapGoal; goal != applyMemoryLimitHeapGoalHeadroom(512<<20) {
+ t.Errorf("heap goal is not the heap limit: %d", goal)
+ }
+ if n >= 25 {
+ // At this alloc/scan rate, the pacer should be extremely close to the goal utilization,
+ // even with the additional memory pressure.
+ assertInEpsilon(t, "GC utilization", c[n-1].gcUtilization, GCGoalUtilization, 0.005)
+
+ // Make sure the pacer settles into a non-degenerate state in at least 25 GC cycles and
+ // that it's meeting its goal.
+ assertInEpsilon(t, "GC utilization", c[n-1].gcUtilization, c[n-2].gcUtilization, 0.005)
+ assertInRange(t, "goal ratio", c[n-1].goalRatio(), 0.95, 1.05)
+ }
+ },
+ },
+ // TODO(mknyszek): Write a test that exercises the pacer's hard goal.
+ // This is difficult in the idealized model this testing framework places
+ // the pacer in, because the calculated overshoot is directly proportional
+ // to the runway for the case of the expected work.
+ // However, it is still possible to trigger this case if something exceptional
+ // happens between calls to revise; the framework just doesn't support this yet.
+ } {
+ e := e
+ t.Run(e.name, func(t *testing.T) {
+ t.Parallel()
+
+ c := NewGCController(e.gcPercent, e.memoryLimit)
+ var bytesAllocatedBlackLast int64
+ results := make([]gcCycleResult, 0, e.length)
+ for i := 0; i < e.length; i++ {
+ cycle := e.next()
+ c.StartCycle(cycle.stackBytes, e.globalsBytes, cycle.scannableFrac, e.nCores)
+
+ // Update pacer incrementally as we complete scan work.
+ const (
+ revisePeriod = 500 * time.Microsecond
+ rateConv = 1024 * float64(revisePeriod) / float64(time.Millisecond)
+ )
+ var nextHeapMarked int64
+ if i == 0 {
+ nextHeapMarked = initialHeapBytes
+ } else {
+ nextHeapMarked = int64(float64(int64(c.HeapMarked())-bytesAllocatedBlackLast) * cycle.growthRate)
+ }
+ globalsScanWorkLeft := int64(e.globalsBytes)
+ stackScanWorkLeft := int64(cycle.stackBytes)
+ heapScanWorkLeft := int64(float64(nextHeapMarked) * cycle.scannableFrac)
+ doWork := func(work int64) (int64, int64, int64) {
+ var deltas [3]int64
+
+ // Do globals work first, then stacks, then heap.
+ for i, workLeft := range []*int64{&globalsScanWorkLeft, &stackScanWorkLeft, &heapScanWorkLeft} {
+ if *workLeft == 0 {
+ continue
+ }
+ if *workLeft > work {
+ deltas[i] += work
+ *workLeft -= work
+ work = 0
+ break
+ } else {
+ deltas[i] += *workLeft
+ work -= *workLeft
+ *workLeft = 0
+ }
+ }
+ return deltas[0], deltas[1], deltas[2]
+ }
+ var (
+ gcDuration int64
+ assistTime int64
+ bytesAllocatedBlack int64
+ )
+ for heapScanWorkLeft+stackScanWorkLeft+globalsScanWorkLeft > 0 {
+ // Simulate GC assist pacing.
+ //
+ // Note that this is an idealized view of the GC assist pacing
+ // mechanism.
+
+ // From the assist ratio and the alloc and scan rates, we can idealize what
+ // the GC CPU utilization looks like.
+ //
+ // We start with assistRatio = (bytes of scan work) / (bytes of runway) (by definition).
+ //
+ // Over revisePeriod, we can also calculate how many bytes are scanned and
+ // allocated, given some GC CPU utilization u:
+ //
+ // bytesScanned = scanRate * rateConv * nCores * u
+ // bytesAllocated = allocRate * rateConv * nCores * (1 - u)
+ //
+ // During revisePeriod, assistRatio is kept constant, and GC assists kick in to
+ // maintain it. Specifically, they act to prevent too many bytes being allocated
+ // compared to how many bytes are scanned. It directly defines the ratio of
+ // bytesScanned to bytesAllocated over this period, hence:
+ //
+ // assistRatio = bytesScanned / bytesAllocated
+ //
+ // From this, we can solve for utilization, because everything else has already
+ // been determined:
+ //
+ // assistRatio = (scanRate * rateConv * nCores * u) / (allocRate * rateConv * nCores * (1 - u))
+ // assistRatio = (scanRate * u) / (allocRate * (1 - u))
+ // assistRatio * allocRate * (1-u) = scanRate * u
+ // assistRatio * allocRate - assistRatio * allocRate * u = scanRate * u
+ // assistRatio * allocRate = assistRatio * allocRate * u + scanRate * u
+ // assistRatio * allocRate = (assistRatio * allocRate + scanRate) * u
+ // u = (assistRatio * allocRate) / (assistRatio * allocRate + scanRate)
+ //
+ // Note that this may give a utilization that is _less_ than GCBackgroundUtilization,
+ // which isn't possible in practice because of dedicated workers. Thus, this case
+ // must be interpreted as GC assists not kicking in at all, and just round up. All
+ // downstream values will then have this accounted for.
+ assistRatio := c.AssistWorkPerByte()
+ utilization := assistRatio * cycle.allocRate / (assistRatio*cycle.allocRate + cycle.scanRate)
+ if utilization < GCBackgroundUtilization {
+ utilization = GCBackgroundUtilization
+ }
+
+ // Knowing the utilization, calculate bytesScanned and bytesAllocated.
+ bytesScanned := int64(cycle.scanRate * rateConv * float64(e.nCores) * utilization)
+ bytesAllocated := int64(cycle.allocRate * rateConv * float64(e.nCores) * (1 - utilization))
+
+ // Subtract work from our model.
+ globalsScanned, stackScanned, heapScanned := doWork(bytesScanned)
+
+ // doWork may not use all of bytesScanned.
+ // In this case, the GC actually ends sometime in this period.
+ // Let's figure out when, exactly, and adjust bytesAllocated too.
+ actualElapsed := revisePeriod
+ actualAllocated := bytesAllocated
+ if actualScanned := globalsScanned + stackScanned + heapScanned; actualScanned < bytesScanned {
+ // actualScanned = scanRate * rateConv * (t / revisePeriod) * nCores * u
+ // => t = actualScanned * revisePeriod / (scanRate * rateConv * nCores * u)
+ actualElapsed = time.Duration(float64(actualScanned) * float64(revisePeriod) / (cycle.scanRate * rateConv * float64(e.nCores) * utilization))
+ actualAllocated = int64(cycle.allocRate * rateConv * float64(actualElapsed) / float64(revisePeriod) * float64(e.nCores) * (1 - utilization))
+ }
+
+ // Ask the pacer to revise.
+ c.Revise(GCControllerReviseDelta{
+ HeapLive: actualAllocated,
+ HeapScan: int64(float64(actualAllocated) * cycle.scannableFrac),
+ HeapScanWork: heapScanned,
+ StackScanWork: stackScanned,
+ GlobalsScanWork: globalsScanned,
+ })
+
+ // Accumulate variables.
+ assistTime += int64(float64(actualElapsed) * float64(e.nCores) * (utilization - GCBackgroundUtilization))
+ gcDuration += int64(actualElapsed)
+ bytesAllocatedBlack += actualAllocated
+ }
+
+ // Put together the results, log them, and concatenate them.
+ result := gcCycleResult{
+ cycle: i + 1,
+ heapLive: c.HeapMarked(),
+ heapScannable: int64(float64(int64(c.HeapMarked())-bytesAllocatedBlackLast) * cycle.scannableFrac),
+ heapTrigger: c.Triggered(),
+ heapPeak: c.HeapLive(),
+ heapGoal: c.HeapGoal(),
+ gcUtilization: float64(assistTime)/(float64(gcDuration)*float64(e.nCores)) + GCBackgroundUtilization,
+ }
+ t.Log("GC", result.String())
+ results = append(results, result)
+
+ // Run the checker for this test.
+ e.check(t, results)
+
+ c.EndCycle(uint64(nextHeapMarked+bytesAllocatedBlack), assistTime, gcDuration, e.nCores)
+
+ bytesAllocatedBlackLast = bytesAllocatedBlack
+ }
+ })
+ }
+}
+
+type gcExecTest struct {
+ name string
+
+ gcPercent int
+ memoryLimit int64
+ globalsBytes uint64
+ nCores int
+
+ allocRate float64Stream // > 0, KiB / cpu-ms
+ scanRate float64Stream // > 0, KiB / cpu-ms
+ growthRate float64Stream // > 0
+ scannableFrac float64Stream // Clamped to [0, 1]
+ stackBytes float64Stream // Multiple of 2048.
+ length int
+
+ checker func(*testing.T, []gcCycleResult)
+}
+
+// minRate is an arbitrary minimum for allocRate, scanRate, and growthRate.
+// These values just cannot be zero.
+const minRate = 0.0001
+
+func (e *gcExecTest) next() gcCycle {
+ return gcCycle{
+ allocRate: e.allocRate.min(minRate)(),
+ scanRate: e.scanRate.min(minRate)(),
+ growthRate: e.growthRate.min(minRate)(),
+ scannableFrac: e.scannableFrac.limit(0, 1)(),
+ stackBytes: uint64(e.stackBytes.quantize(2048).min(0)()),
+ }
+}
+
+func (e *gcExecTest) check(t *testing.T, results []gcCycleResult) {
+ t.Helper()
+
+ // Do some basic general checks first.
+ n := len(results)
+ switch n {
+ case 0:
+ t.Fatal("no results passed to check")
+ return
+ case 1:
+ if results[0].cycle != 1 {
+ t.Error("first cycle has incorrect number")
+ }
+ default:
+ if results[n-1].cycle != results[n-2].cycle+1 {
+ t.Error("cycle numbers out of order")
+ }
+ }
+ if u := results[n-1].gcUtilization; u < 0 || u > 1 {
+ t.Fatal("GC utilization not within acceptable bounds")
+ }
+ if s := results[n-1].heapScannable; s < 0 {
+ t.Fatal("heapScannable is negative")
+ }
+ if e.checker == nil {
+ t.Fatal("test-specific checker is missing")
+ }
+
+ // Run the test-specific checker.
+ e.checker(t, results)
+}
+
+type gcCycle struct {
+ allocRate float64
+ scanRate float64
+ growthRate float64
+ scannableFrac float64
+ stackBytes uint64
+}
+
+type gcCycleResult struct {
+ cycle int
+
+ // These come directly from the pacer, so uint64.
+ heapLive uint64
+ heapTrigger uint64
+ heapGoal uint64
+ heapPeak uint64
+
+ // These are produced by the simulation, so int64 and
+ // float64 are more appropriate, so that we can check for
+ // bad states in the simulation.
+ heapScannable int64
+ gcUtilization float64
+}
+
+func (r *gcCycleResult) goalRatio() float64 {
+ return float64(r.heapPeak) / float64(r.heapGoal)
+}
+
+func (r *gcCycleResult) runway() float64 {
+ return float64(r.heapGoal - r.heapTrigger)
+}
+
+func (r *gcCycleResult) triggerRatio() float64 {
+ return float64(r.heapTrigger-r.heapLive) / float64(r.heapGoal-r.heapLive)
+}
+
+func (r *gcCycleResult) String() string {
+ return fmt.Sprintf("%d %2.1f%% %d->%d->%d (goal: %d)", r.cycle, r.gcUtilization*100, r.heapLive, r.heapTrigger, r.heapPeak, r.heapGoal)
+}
+
+func assertInEpsilon(t *testing.T, name string, a, b, epsilon float64) {
+ t.Helper()
+ assertInRange(t, name, a, b-epsilon, b+epsilon)
+}
+
+func assertInRange(t *testing.T, name string, a, min, max float64) {
+ t.Helper()
+ if a < min || a > max {
+ t.Errorf("%s not in range (%f, %f): %f", name, min, max, a)
+ }
+}
+
+// float64Stream is a function that generates an infinite stream of
+// float64 values when called repeatedly.
+type float64Stream func() float64
+
+// constant returns a stream that generates the value c.
+func constant(c float64) float64Stream {
+ return func() float64 {
+ return c
+ }
+}
+
+// unit returns a stream that generates a single peak with
+// amplitude amp, followed by zeroes.
+//
+// In another manner of speaking, this is the Kronecker delta.
+func unit(amp float64) float64Stream {
+ dropped := false
+ return func() float64 {
+ if dropped {
+ return 0
+ }
+ dropped = true
+ return amp
+ }
+}
+
+// oscillate returns a stream that oscillates sinusoidally
+// with the given amplitude, phase, and period.
+func oscillate(amp, phase float64, period int) float64Stream {
+ var cycle int
+ return func() float64 {
+ p := float64(cycle)/float64(period)*2*math.Pi + phase
+ cycle++
+ if cycle == period {
+ cycle = 0
+ }
+ return math.Sin(p) * amp
+ }
+}
+
+// ramp returns a stream that moves from zero to height
+// over the course of length steps.
+func ramp(height float64, length int) float64Stream {
+ var cycle int
+ return func() float64 {
+ h := height * float64(cycle) / float64(length)
+ if cycle < length {
+ cycle++
+ }
+ return h
+ }
+}
+
+// random returns a stream that generates random numbers
+// between -amp and amp.
+func random(amp float64, seed int64) float64Stream {
+ r := rand.New(rand.NewSource(seed))
+ return func() float64 {
+ return ((r.Float64() - 0.5) * 2) * amp
+ }
+}
+
+// delay returns a new stream which is a buffered version
+// of f: it returns zero for cycles steps, followed by f.
+func (f float64Stream) delay(cycles int) float64Stream {
+ zeroes := 0
+ return func() float64 {
+ if zeroes < cycles {
+ zeroes++
+ return 0
+ }
+ return f()
+ }
+}
+
+// scale returns a new stream that is f, but attenuated by a
+// constant factor.
+func (f float64Stream) scale(amt float64) float64Stream {
+ return func() float64 {
+ return f() * amt
+ }
+}
+
+// offset returns a new stream that is f but offset by amt
+// at each step.
+func (f float64Stream) offset(amt float64) float64Stream {
+ return func() float64 {
+ old := f()
+ return old + amt
+ }
+}
+
+// sum returns a new stream that is the sum of all input streams
+// at each step.
+func (f float64Stream) sum(fs ...float64Stream) float64Stream {
+ return func() float64 {
+ sum := f()
+ for _, s := range fs {
+ sum += s()
+ }
+ return sum
+ }
+}
+
+// quantize returns a new stream that rounds f to a multiple
+// of mult at each step.
+func (f float64Stream) quantize(mult float64) float64Stream {
+ return func() float64 {
+ r := f() / mult
+ if r < 0 {
+ return math.Ceil(r) * mult
+ }
+ return math.Floor(r) * mult
+ }
+}
+
+// min returns a new stream that replaces all values produced
+// by f lower than min with min.
+func (f float64Stream) min(min float64) float64Stream {
+ return func() float64 {
+ return math.Max(min, f())
+ }
+}
+
+// max returns a new stream that replaces all values produced
+// by f higher than max with max.
+func (f float64Stream) max(max float64) float64Stream {
+ return func() float64 {
+ return math.Min(max, f())
+ }
+}
+
+// limit returns a new stream that replaces all values produced
+// by f lower than min with min and higher than max with max.
+func (f float64Stream) limit(min, max float64) float64Stream {
+ return func() float64 {
+ v := f()
+ if v < min {
+ v = min
+ } else if v > max {
+ v = max
+ }
+ return v
+ }
+}
+
+func applyMemoryLimitHeapGoalHeadroom(goal uint64) uint64 {
+ headroom := goal / 100 * MemoryLimitHeapGoalHeadroomPercent
+ if headroom < MemoryLimitMinHeapGoalHeadroom {
+ headroom = MemoryLimitMinHeapGoalHeadroom
+ }
+ if goal < headroom || goal-headroom < headroom {
+ goal = headroom
+ } else {
+ goal -= headroom
+ }
+ return goal
+}
+
+func TestIdleMarkWorkerCount(t *testing.T) {
+ const workers = 10
+ c := NewGCController(100, math.MaxInt64)
+ c.SetMaxIdleMarkWorkers(workers)
+ for i := 0; i < workers; i++ {
+ if !c.NeedIdleMarkWorker() {
+ t.Fatalf("expected to need idle mark workers: i=%d", i)
+ }
+ if !c.AddIdleMarkWorker() {
+ t.Fatalf("expected to be able to add an idle mark worker: i=%d", i)
+ }
+ }
+ if c.NeedIdleMarkWorker() {
+ t.Fatalf("expected to not need idle mark workers")
+ }
+ if c.AddIdleMarkWorker() {
+ t.Fatalf("expected to not be able to add an idle mark worker")
+ }
+ for i := 0; i < workers; i++ {
+ c.RemoveIdleMarkWorker()
+ if !c.NeedIdleMarkWorker() {
+ t.Fatalf("expected to need idle mark workers after removal: i=%d", i)
+ }
+ }
+ for i := 0; i < workers-1; i++ {
+ if !c.AddIdleMarkWorker() {
+ t.Fatalf("expected to be able to add idle mark workers after adding again: i=%d", i)
+ }
+ }
+ for i := 0; i < 10; i++ {
+ if !c.AddIdleMarkWorker() {
+ t.Fatalf("expected to be able to add idle mark workers interleaved: i=%d", i)
+ }
+ if c.AddIdleMarkWorker() {
+ t.Fatalf("expected to not be able to add idle mark workers interleaved: i=%d", i)
+ }
+ c.RemoveIdleMarkWorker()
+ }
+ // Support the max being below the count.
+ c.SetMaxIdleMarkWorkers(0)
+ if c.NeedIdleMarkWorker() {
+ t.Fatalf("expected to not need idle mark workers after capacity set to 0")
+ }
+ if c.AddIdleMarkWorker() {
+ t.Fatalf("expected to not be able to add idle mark workers after capacity set to 0")
+ }
+ for i := 0; i < workers-1; i++ {
+ c.RemoveIdleMarkWorker()
+ }
+ if c.NeedIdleMarkWorker() {
+ t.Fatalf("expected to not need idle mark workers after capacity set to 0")
+ }
+ if c.AddIdleMarkWorker() {
+ t.Fatalf("expected to not be able to add idle mark workers after capacity set to 0")
+ }
+ c.SetMaxIdleMarkWorkers(1)
+ if !c.NeedIdleMarkWorker() {
+ t.Fatalf("expected to need idle mark workers after capacity set to 1")
+ }
+ if !c.AddIdleMarkWorker() {
+ t.Fatalf("expected to be able to add idle mark workers after capacity set to 1")
+ }
+}
generated by cgit v1.2.3 (git 2.39.1) at 2024-11-25 21:57:56 +0000