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runtime: add comments for gcCPULimiter testcases #76069

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runtime: add comments for gcCPULimiter testcases #76069

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35 changes: 35 additions & 0 deletions src/runtime/mgclimit_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -154,6 +154,22 @@ func TestGCCPULimiter(t *testing.T) {
// Drain the bucket by half.
l.AddAssistTime(assistTime(CapacityPerProc, 0))
l.Update(advance(CapacityPerProc))
//
// test start condition: l.Fill == l.Capacity
//
// assistTime = 0
// gcTime = CapacityPerProc * procs * GCBackgroundUtilization
// mutatorTime = CapacityPerProc * procs * (1 - GCBackgroundUtilization)
// change = gcTime - mutatorTime
// = CapacityPerProc * procs * (2 * GCBackgroundUtilization - 1)
// l.Fill = l.Fill + change // here change < 0
// = l.Capacity + change
// = CapacityPerProc * procs + change
// = CapacityPerProc * procs * 2 * GCBackgroundUtilization
// = l.Capacity * 2 * GCBackgroundUtilization
// = l.Capacity * 0.5 // by default GCBackgroundUtilization = 0.25
// = l.Capacity / 2
//
if expect := l.Capacity() / 2; l.Fill() != expect {
t.Errorf("failed to drain to %d, got fill %d", expect, l.Fill())
}
Expand All @@ -167,6 +183,25 @@ func TestGCCPULimiter(t *testing.T) {
// Test overfilling the bucket.
l.AddAssistTime(assistTime(CapacityPerProc, 1.0-GCBackgroundUtilization))
l.Update(advance(CapacityPerProc))
//
// test start condition: l.Fill == l.Capacity * 2 * GCBackgroundUtilization
//
// assistTime = CapacityPerProc * procs * (1 - GCBackgroundUtilization)
// gcTime = CapacityPerProc * procs * GCBackgroundUtilization + assistTime
// = CapacityPerProc * procs
// = l.Capacity
// mutatorTime = CapacityPerProc * procs * (1 - GCBackgroundUtilization) - assistTime
// = 0
// change = gcTime - mutatorTime
// = l.Capacity
// l.Overflow = l.Fill + change - l.Capacity
// = l.Capacity * 2 * GCBackgroundUtilization + l.Capacity - l.Capacity
// = l.Capacity * 2 * GCBackgroundUtilization
// = l.Capacity * 0.5 // by default GCBackgroundUtilization = 0.25
// = l.Capacity / 2
// = CapacityPerProc * procs / 2
// l.Fill = l.Capacity // because change is too large
//
if l.Fill() != l.Capacity() {
t.Errorf("failed to fill to capacity %d, got fill %d", l.Capacity(), l.Fill())
}
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