amadan
carlos / todomvc-bakeoff Public
fix: slow-down point ignores a one-step latency blip
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
2 files changed,
+26
−5
harness/harness_test.go+7 −0harness/sweep.go+19 −5
diff --git a/harness/harness_test.go b/harness/harness_test.go| index 57304b8..0b43b70 100644 |
| --- a/harness/harness_test.go |
| +++ b/harness/harness_test.go |
| @@ -301,3 +301,10 @@ func TestSweepStopsOnErrorsOrFlatThroughput(t *testing.T) { |
| t.Fatal("one flat step then growth: keep going") |
| } |
| } |
| + |
| +func TestKneeIgnoresAOneStepBlip(t *testing.T) { |
| + sweep := []LoadResult{lr(1, 58, 29, 0), lr(2, 108, 38, 0), lr(4, 98, 66, 0), lr(8, 184, 77, 0), lr(16, 314, 97, 0), lr(32, 325, 294, 0), lr(64, 324, 640, 0)} |
| + if k := Knee(sweep); !k.Found || k.Concurrency != 16 || k.PeakRPS != 325 { |
| + t.Fatalf("got %+v, want 16: the fewest connections from which no more load adds 10%%", k) |
| + } |
| +} |
diff --git a/harness/sweep.go b/harness/sweep.go| index 1075202..c2aefc9 100644 |
| --- a/harness/sweep.go |
| +++ b/harness/sweep.go |
| @@ -19,17 +19,31 @@ type KneeResult struct { |
| MaxTested int |
| } |
| -// Knee finds the first doubling that raised throughput by less than 10%: |
| -// the app slows down past the level before it. |
| +// Knee finds where the app slows down: the fewest connections from which |
| +// no further load in the sweep raised throughput by 10% or more. A single |
| +// noisy step can't end the search early, because later growth resets it. |
| func Knee(sweep []LoadResult) KneeResult { |
| var k KneeResult |
| - for i, r := range sweep { |
| + for _, r := range sweep { |
| if r.RPS > k.PeakRPS { |
| k.PeakRPS = r.RPS |
| } |
| k.MaxTested = r.Concurrency |
| - if !k.Found && i > 0 && r.RPS < sweep[i-1].RPS*flatGain { |
| - k.Found, k.Concurrency, k.P50Ms = true, sweep[i-1].Concurrency, sweep[i-1].P50Ms |
| + } |
| + for i, r := range sweep { |
| + if i == len(sweep)-1 { |
| + break |
| + } |
| + gains := false |
| + for _, later := range sweep[i+1:] { |
| + if later.RPS >= r.RPS*flatGain { |
| + gains = true |
| + break |
| + } |
| + } |
| + if !gains { |
| + k.Found, k.Concurrency, k.P50Ms = true, r.Concurrency, r.P50Ms |
| + break |
| } |
| } |
| return k |