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runtime,runtime/metrics: use explicit histogram boundaries

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This change modifies the semantics of
runtime/metrics.Float64Histogram.Buckets to remove implicit buckets to
that extend to positive and negative infinity and instead defines all
bucket boundaries as explicitly listed.

Bucket boundaries remain the same as before except
/gc/heap/allocs-by-size:objects and /gc/heap/frees-by-size:objects no
longer have a bucket that extends to negative infinity.

This change simplifies the Float64Histogram API, making it both easier
to understand and easier to use.

Also, add a test for allocs-by-size and frees-by-size that checks them
against MemStats.

Fixes #43443.

Change-Id: I5620f15bd084562dadf288f733c4a8cace21910c
Reviewed-on: https://go-review.googlesource.com/c/go/+/281238
Run-TryBot: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>
Reviewed-by: Michael Pratt <mpratt@google.com>
Trust: Michael Knyszek <mknyszek@google.com>
This commit is contained in:
Michael Anthony Knyszek 2021-01-06 23:05:22 +00:00 • committed by Michael Knyszek
parent a9ccd2d795
commit ae97717133
4 changed files with 99 additions and 30 deletions
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32
src/runtime/metrics.go
View file

@ -41,8 +41,13 @@ func initMetrics() {
if metricsInit {
return
}
sizeClassBuckets = make([]float64, _NumSizeClasses)
for i := range sizeClassBuckets {
sizeClassBuckets = make([]float64, _NumSizeClasses, _NumSizeClasses+1)
// Skip size class 0 which is a stand-in for large objects, but large
// objects are tracked separately (and they actually get placed in
// the last bucket, not the first).
sizeClassBuckets[0] = 1 // The smallest allocation is 1 byte in size.
for i := 1; i < _NumSizeClasses; 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
@ -56,6 +61,8 @@ func initMetrics() {
// boundaries.
sizeClassBuckets[i] = float64(class_to_size[i] + 1)
}
sizeClassBuckets = append(sizeClassBuckets, float64Inf())
timeHistBuckets = timeHistogramMetricsBuckets()
metrics = map[string]metricData{
"/gc/cycles/automatic:gc-cycles": {
@ -84,8 +91,10 @@ func initMetrics() {
compute: func(in *statAggregate, out *metricValue) {
hist := out.float64HistOrInit(sizeClassBuckets)
hist.counts[len(hist.counts)-1] = uint64(in.heapStats.largeAllocCount)
for i := range hist.buckets {
hist.counts[i] = uint64(in.heapStats.smallAllocCount[i])
// Cut off the first index which is ostensibly for size class 0,
// but large objects are tracked separately so it's actually unused.
for i, count := range in.heapStats.smallAllocCount[1:] {
hist.counts[i] = uint64(count)
}
},
},
@ -94,8 +103,10 @@ func initMetrics() {
compute: func(in *statAggregate, out *metricValue) {
hist := out.float64HistOrInit(sizeClassBuckets)
hist.counts[len(hist.counts)-1] = uint64(in.heapStats.largeFreeCount)
for i := range hist.buckets {
hist.counts[i] = uint64(in.heapStats.smallFreeCount[i])
// Cut off the first index which is ostensibly for size class 0,
// but large objects are tracked separately so it's actually unused.
for i, count := range in.heapStats.smallFreeCount[1:] {
hist.counts[i] = uint64(count)
}
},
},
@ -116,8 +127,11 @@ func initMetrics() {
"/gc/pauses:seconds": {
compute: func(_ *statAggregate, out *metricValue) {
hist := out.float64HistOrInit(timeHistBuckets)
// The bottom-most bucket, containing negative values, is tracked
// as a separately as underflow, so fill that in manually and then
// iterate over the rest.
hist.counts[0] = atomic.Load64(&memstats.gcPauseDist.underflow)
for i := range hist.buckets {
for i := range memstats.gcPauseDist.counts {
hist.counts[i+1] = atomic.Load64(&memstats.gcPauseDist.counts[i])
}
},
@ -437,8 +451,8 @@ func (v *metricValue) float64HistOrInit(buckets []float64) *metricFloat64Histogr
v.pointer = unsafe.Pointer(hist)
}
hist.buckets = buckets
if len(hist.counts) != len(hist.buckets)+1 {
hist.counts = make([]uint64, len(buckets)+1)
if len(hist.counts) != len(hist.buckets)-1 {
hist.counts = make([]uint64, len(buckets)-1)
}
return hist
}