runtime: raise alert threshold on window smhasher test

This alert is triggering occasionally. I've investigated the
collisions that happen, and they all seem to be pairwise, so they are
not a big deal.  "pairwise" = when there are 32 collisions, it is two
keys mapping to the same hash, 32 times, not 33 keys all mapping to
the same hash.

Add some t.Logf calls in case this comes back, which will help isolate
the problem.

Fixes #39352

Change-Id: I1749d7c8efd0afcf9024d8964d15bc0f58a86e4f
Reviewed-on: https://go-review.googlesource.com/c/go/+/237718
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

diff --git a/src/runtime/hash_test.go b/src/runtime/hash_test.go
index 655ca18f11579f18de4de5018b54b680b65d02d5..502383557b803111c5d69e0488037d6664231a88 100644 (file)
--- a/src/runtime/hash_test.go
+++ b/src/runtime/hash_test.go
@@ -152,14 +152,13 @@ func (s *HashSet) addS_seed(x string, seed uintptr) {
        s.add(StringHash(x, seed))
 }
 func (s *HashSet) check(t *testing.T) {
-       const SLOP = 10.0
+       const SLOP = 50.0
        collisions := s.n - len(s.m)
-       //fmt.Printf("%d/%d\n", len(s.m), s.n)
        pairs := int64(s.n) * int64(s.n-1) / 2
        expected := float64(pairs) / math.Pow(2.0, float64(hashSize))
        stddev := math.Sqrt(expected)
        if float64(collisions) > expected+SLOP*(3*stddev+1) {
-               t.Errorf("unexpected number of collisions: got=%d mean=%f stddev=%f", collisions, expected, stddev)
+               t.Errorf("unexpected number of collisions: got=%d mean=%f stddev=%f threshold=%f", collisions, expected, stddev, expected+SLOP*(3*stddev+1))
        }
 }
 
@@ -564,8 +563,11 @@ func avalancheTest1(t *testing.T, k Key) {
 
 // All bit rotations of a set of distinct keys
 func TestSmhasherWindowed(t *testing.T) {
+       t.Logf("32 bit keys")
        windowed(t, &Int32Key{})
+       t.Logf("64 bit keys")
        windowed(t, &Int64Key{})
+       t.Logf("string keys")
        windowed(t, &BytesKey{make([]byte, 128)})
 }
 func windowed(t *testing.T, k Key) {