mirror of https://go.googlesource.com/go
256 lines
9.0 KiB
Go
256 lines
9.0 KiB
Go
// Copyright 2022 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package runtime_test
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import (
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. "runtime"
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"testing"
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"time"
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)
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func TestGCCPULimiter(t *testing.T) {
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const procs = 14
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// Create mock time.
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ticks := int64(0)
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advance := func(d time.Duration) int64 {
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t.Helper()
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ticks += int64(d)
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return ticks
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}
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// assistTime computes the CPU time for assists using frac of GOMAXPROCS
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// over the wall-clock duration d.
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assistTime := func(d time.Duration, frac float64) int64 {
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t.Helper()
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return int64(frac * float64(d) * procs)
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}
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l := NewGCCPULimiter(ticks, procs)
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// Do the whole test twice to make sure state doesn't leak across.
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var baseOverflow uint64 // Track total overflow across iterations.
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for i := 0; i < 2; i++ {
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t.Logf("Iteration %d", i+1)
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if l.Capacity() != procs*CapacityPerProc {
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t.Fatalf("unexpected capacity: %d", l.Capacity())
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}
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if l.Fill() != 0 {
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t.Fatalf("expected empty bucket to start")
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}
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// Test filling the bucket with just mutator time.
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l.Update(advance(10 * time.Millisecond))
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l.Update(advance(1 * time.Second))
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l.Update(advance(1 * time.Hour))
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if l.Fill() != 0 {
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t.Fatalf("expected empty bucket from only accumulating mutator time, got fill of %d cpu-ns", l.Fill())
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}
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// Test needUpdate.
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if l.NeedUpdate(advance(GCCPULimiterUpdatePeriod / 2)) {
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t.Fatal("need update even though updated half a period ago")
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}
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if !l.NeedUpdate(advance(GCCPULimiterUpdatePeriod)) {
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t.Fatal("doesn't need update even though updated 1.5 periods ago")
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}
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l.Update(advance(0))
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if l.NeedUpdate(advance(0)) {
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t.Fatal("need update even though just updated")
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}
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// Test transitioning the bucket to enable the GC.
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l.StartGCTransition(true, advance(109*time.Millisecond))
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l.FinishGCTransition(advance(2*time.Millisecond + 1*time.Microsecond))
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if expect := uint64((2*time.Millisecond + 1*time.Microsecond) * procs); l.Fill() != expect {
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t.Fatalf("expected fill of %d, got %d cpu-ns", expect, l.Fill())
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}
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// Test passing time without assists during a GC. Specifically, just enough to drain the bucket to
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// exactly procs nanoseconds (easier to get to because of rounding).
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//
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// The window we need to drain the bucket is 1/(1-2*gcBackgroundUtilization) times the current fill:
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//
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// fill + (window * procs * gcBackgroundUtilization - window * procs * (1-gcBackgroundUtilization)) = n
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// fill = n - (window * procs * gcBackgroundUtilization - window * procs * (1-gcBackgroundUtilization))
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// fill = n + window * procs * ((1-gcBackgroundUtilization) - gcBackgroundUtilization)
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// fill = n + window * procs * (1-2*gcBackgroundUtilization)
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// window = (fill - n) / (procs * (1-2*gcBackgroundUtilization)))
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//
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// And here we want n=procs:
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factor := (1 / (1 - 2*GCBackgroundUtilization))
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fill := (2*time.Millisecond + 1*time.Microsecond) * procs
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l.Update(advance(time.Duration(factor * float64(fill-procs) / procs)))
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if l.Fill() != procs {
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t.Fatalf("expected fill %d cpu-ns from draining after a GC started, got fill of %d cpu-ns", procs, l.Fill())
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}
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// Drain to zero for the rest of the test.
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l.Update(advance(2 * procs * CapacityPerProc))
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if l.Fill() != 0 {
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t.Fatalf("expected empty bucket from draining, got fill of %d cpu-ns", l.Fill())
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}
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// Test filling up the bucket with 50% total GC work (so, not moving the bucket at all).
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l.AddAssistTime(assistTime(10*time.Millisecond, 0.5-GCBackgroundUtilization))
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l.Update(advance(10 * time.Millisecond))
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if l.Fill() != 0 {
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t.Fatalf("expected empty bucket from 50%% GC work, got fill of %d cpu-ns", l.Fill())
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}
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// Test adding to the bucket overall with 100% GC work.
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l.AddAssistTime(assistTime(time.Millisecond, 1.0-GCBackgroundUtilization))
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l.Update(advance(time.Millisecond))
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if expect := uint64(procs * time.Millisecond); l.Fill() != expect {
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t.Errorf("expected %d fill from 100%% GC CPU, got fill of %d cpu-ns", expect, l.Fill())
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}
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if l.Limiting() {
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t.Errorf("limiter is enabled after filling bucket but shouldn't be")
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}
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if t.Failed() {
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t.FailNow()
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}
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// Test filling the bucket exactly full.
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l.AddAssistTime(assistTime(CapacityPerProc-time.Millisecond, 1.0-GCBackgroundUtilization))
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l.Update(advance(CapacityPerProc - time.Millisecond))
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if l.Fill() != l.Capacity() {
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t.Errorf("expected bucket filled to capacity %d, got %d", l.Capacity(), l.Fill())
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}
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if !l.Limiting() {
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t.Errorf("limiter is not enabled after filling bucket but should be")
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}
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if l.Overflow() != 0+baseOverflow {
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t.Errorf("bucket filled exactly should not have overflow, found %d", l.Overflow())
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}
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if t.Failed() {
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t.FailNow()
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}
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// Test adding with a delta of exactly zero. That is, GC work is exactly 50% of all resources.
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// Specifically, the limiter should still be on, and no overflow should accumulate.
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l.AddAssistTime(assistTime(1*time.Second, 0.5-GCBackgroundUtilization))
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l.Update(advance(1 * time.Second))
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if l.Fill() != l.Capacity() {
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t.Errorf("expected bucket filled to capacity %d, got %d", l.Capacity(), l.Fill())
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}
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if !l.Limiting() {
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t.Errorf("limiter is not enabled after filling bucket but should be")
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}
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if l.Overflow() != 0+baseOverflow {
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t.Errorf("bucket filled exactly should not have overflow, found %d", l.Overflow())
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}
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if t.Failed() {
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t.FailNow()
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}
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// Drain the bucket by half.
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l.AddAssistTime(assistTime(CapacityPerProc, 0))
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l.Update(advance(CapacityPerProc))
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if expect := l.Capacity() / 2; l.Fill() != expect {
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t.Errorf("failed to drain to %d, got fill %d", expect, l.Fill())
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}
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if l.Limiting() {
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t.Errorf("limiter is enabled after draining bucket but shouldn't be")
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}
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if t.Failed() {
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t.FailNow()
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}
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// Test overfilling the bucket.
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l.AddAssistTime(assistTime(CapacityPerProc, 1.0-GCBackgroundUtilization))
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l.Update(advance(CapacityPerProc))
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if l.Fill() != l.Capacity() {
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t.Errorf("failed to fill to capacity %d, got fill %d", l.Capacity(), l.Fill())
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}
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if !l.Limiting() {
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t.Errorf("limiter is not enabled after overfill but should be")
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}
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if expect := uint64(CapacityPerProc * procs / 2); l.Overflow() != expect+baseOverflow {
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t.Errorf("bucket overfilled should have overflow %d, found %d", expect, l.Overflow())
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}
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if t.Failed() {
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t.FailNow()
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}
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// Test ending the cycle with some assists left over.
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l.AddAssistTime(assistTime(1*time.Millisecond, 1.0-GCBackgroundUtilization))
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l.StartGCTransition(false, advance(1*time.Millisecond))
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if l.Fill() != l.Capacity() {
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t.Errorf("failed to maintain fill to capacity %d, got fill %d", l.Capacity(), l.Fill())
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}
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if !l.Limiting() {
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t.Errorf("limiter is not enabled after overfill but should be")
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}
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if expect := uint64((CapacityPerProc/2 + time.Millisecond) * procs); l.Overflow() != expect+baseOverflow {
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t.Errorf("bucket overfilled should have overflow %d, found %d", expect, l.Overflow())
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}
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if t.Failed() {
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t.FailNow()
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}
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// Make sure the STW adds to the bucket.
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l.FinishGCTransition(advance(5 * time.Millisecond))
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if l.Fill() != l.Capacity() {
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t.Errorf("failed to maintain fill to capacity %d, got fill %d", l.Capacity(), l.Fill())
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}
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if !l.Limiting() {
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t.Errorf("limiter is not enabled after overfill but should be")
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}
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if expect := uint64((CapacityPerProc/2 + 6*time.Millisecond) * procs); l.Overflow() != expect+baseOverflow {
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t.Errorf("bucket overfilled should have overflow %d, found %d", expect, l.Overflow())
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}
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if t.Failed() {
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t.FailNow()
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}
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// Resize procs up and make sure limiting stops.
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expectFill := l.Capacity()
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l.ResetCapacity(advance(0), procs+10)
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if l.Fill() != expectFill {
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t.Errorf("failed to maintain fill at old capacity %d, got fill %d", expectFill, l.Fill())
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}
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if l.Limiting() {
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t.Errorf("limiter is enabled after resetting capacity higher")
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}
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if expect := uint64((CapacityPerProc/2 + 6*time.Millisecond) * procs); l.Overflow() != expect+baseOverflow {
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t.Errorf("bucket overflow %d should have remained constant, found %d", expect, l.Overflow())
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}
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if t.Failed() {
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t.FailNow()
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}
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// Resize procs down and make sure limiting begins again.
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// Also make sure resizing doesn't affect overflow. This isn't
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// a case where we want to report overflow, because we're not
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// actively doing work to achieve it. It's that we have fewer
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// CPU resources now.
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l.ResetCapacity(advance(0), procs-10)
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if l.Fill() != l.Capacity() {
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t.Errorf("failed lower fill to new capacity %d, got fill %d", l.Capacity(), l.Fill())
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}
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if !l.Limiting() {
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t.Errorf("limiter is disabled after resetting capacity lower")
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}
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if expect := uint64((CapacityPerProc/2 + 6*time.Millisecond) * procs); l.Overflow() != expect+baseOverflow {
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t.Errorf("bucket overflow %d should have remained constant, found %d", expect, l.Overflow())
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}
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if t.Failed() {
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t.FailNow()
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}
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// Get back to a zero state. The top of the loop will double check.
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l.ResetCapacity(advance(CapacityPerProc*procs), procs)
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// Track total overflow for future iterations.
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baseOverflow += uint64((CapacityPerProc/2 + 6*time.Millisecond) * procs)
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}
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}
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