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runtime: fix allocs-by-size and frees-by-size buckets

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Currently these two metrics are reported incorrectly, going by the
documentation in the runtime/metrics package. We just copy in the
size-class-based values from the runtime wholesale, but those implicitly
have an inclusive upper-bound and exclusive lower-bound (e.g. 48-byte
size class contains objects in the size range (32, 48]) but the API
declares inclusive lower-bounds and exclusive upper-bounds.

Also, the bottom bucket representing (-inf, 1) should always be empty.
Extend the consistency check to verify this.

Updates #43329.

Change-Id: I11b5b062a34e13405ab662d15334bda91f779775
Reviewed-on: https://go-review.googlesource.com/c/go/+/279467
Run-TryBot: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Trust: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Michael Pratt <mpratt@google.com>
This commit is contained in:
Michael Anthony Knyszek 2020-12-22 16:23:29 +00:00 • committed by Michael Knyszek
parent fb96f07e1a
commit 8db7e2fecd
2 changed files with 18 additions and 1 deletions
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13
src/runtime/metrics.go
View file

@ -43,7 +43,18 @@ func initMetrics() {
}
sizeClassBuckets = make([]float64, _NumSizeClasses)
for i := range sizeClassBuckets {
sizeClassBuckets[i] = float64(class_to_size[i])
// Size classes have an inclusive upper-bound
// and exclusive lower bound (e.g. 48-byte size class is
// (32, 48]) whereas we want and inclusive lower-bound
// and exclusive upper-bound (e.g. 48-byte size class is
// [33, 49). We can achieve this by shifting all bucket
// boundaries up by 1.
//
// Also, a float64 can precisely represent integers with
// value up to 2^53 and size classes are relatively small
// (nowhere near 2^48 even) so this will give us exact
// boundaries.
sizeClassBuckets[i] = float64(class_to_size[i] + 1)
}
timeHistBuckets = timeHistogramMetricsBuckets()
metrics = map[string]metricData{

6
src/runtime/metrics_test.go
View file

@ -154,6 +154,12 @@ func TestReadMetricsConsistency(t *testing.T) {
if totalVirtual.got != totalVirtual.want {
t.Errorf(`"/memory/classes/total:bytes" does not match sum of /memory/classes/**: got %d, want %d`, totalVirtual.got, totalVirtual.want)
}
if objects.alloc.Counts[0] > 0 {
t.Error("found counts for objects of non-positive size in allocs-by-size")
}
if objects.free.Counts[0] > 0 {
t.Error("found counts for objects of non-positive size in frees-by-size")
}
if len(objects.alloc.Buckets) != len(objects.free.Buckets) {
t.Error("allocs-by-size and frees-by-size buckets don't match in length")
} else if len(objects.alloc.Counts) != len(objects.free.Counts) {