138 lines
3.8 KiB
C++
138 lines
3.8 KiB
C++
/*
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* Histogram.h
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*
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* This source file is part of the FoundationDB open source project
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*
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* Copyright 2013-2018 Apple Inc. and the FoundationDB project authors
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#ifndef FLOW_HISTOGRAM_H
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#define FLOW_HISTOGRAM_H
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#pragma once
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#include <flow/Arena.h>
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#include <string>
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#include <map>
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#include <unordered_map>
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#ifdef _WIN32
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#include <intrin.h>
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#pragma intrinsic(_BitScanReverse)
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#endif
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class Histogram;
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class HistogramRegistry {
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public:
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void registerHistogram(Histogram* h);
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void unregisterHistogram(Histogram* h);
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Histogram* lookupHistogram(std::string name);
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void logReport();
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private:
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// This map is ordered by key so that ops within the same group end up
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// next to each other in the trace log.
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std::map<std::string, Histogram*> histograms;
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};
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HistogramRegistry& GetHistogramRegistry();
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/*
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* A fast histogram with power-of-two spaced buckets.
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*
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* For more information about this technique, see:
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* https://www.fsl.cs.stonybrook.edu/project-osprof.html
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*/
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class Histogram final : public ReferenceCounted<Histogram> {
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public:
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enum class Unit { microseconds, bytes, bytes_per_second };
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private:
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static const std::unordered_map<Unit, std::string> UnitToStringMapper;
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Histogram(std::string group, std::string op, Unit unit, HistogramRegistry& registry)
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: group(group), op(op), unit(unit), registry(registry), ReferenceCounted<Histogram>() {
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ASSERT(UnitToStringMapper.find(unit) != UnitToStringMapper.end());
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clear();
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}
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static std::string generateName(std::string group, std::string op) { return group + ":" + op; }
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public:
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~Histogram() { registry.unregisterHistogram(this); }
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static Reference<Histogram> getHistogram(StringRef group, StringRef op, Unit unit) {
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std::string group_str = group.toString();
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std::string op_str = op.toString();
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std::string name = generateName(group_str, op_str);
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HistogramRegistry& registry = GetHistogramRegistry();
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Histogram* h = registry.lookupHistogram(name);
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if (!h) {
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h = new Histogram(group_str, op_str, unit, registry);
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registry.registerHistogram(h);
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return Reference<Histogram>(h);
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} else {
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return Reference<Histogram>::addRef(h);
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}
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}
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// This histogram buckets samples into powers of two.
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inline void sample(uint32_t sample) {
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size_t idx;
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#ifdef _WIN32
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unsigned long index;
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// _BitScanReverse sets index to the position of the first non-zero bit, so
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// _BitScanReverse(sample) ~= log_2(sample). _BitScanReverse returns false if
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// sample is zero.
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idx = _BitScanReverse(&index, sample) ? index : 0;
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#else
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// __builtin_clz counts the leading zeros in its uint32_t argument. So, 31-clz ~= log_2(sample).
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// __builtin_clz(0) is undefined.
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idx = sample ? (31 - __builtin_clz(sample)) : 0;
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#endif
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ASSERT(idx < 32);
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buckets[idx]++;
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}
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inline void sampleSeconds(double delta) {
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uint64_t delta_usec = (delta * 1000000);
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if (delta_usec > UINT32_MAX) {
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sample(UINT32_MAX);
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} else {
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sample((uint32_t)(delta * 1000000)); // convert to microseconds and truncate to integer
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}
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}
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void clear() {
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for (uint32_t& i : buckets) {
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i = 0;
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}
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}
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void writeToLog();
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std::string name() { return generateName(this->group, this->op); }
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std::string const group;
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std::string const op;
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Unit const unit;
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HistogramRegistry& registry;
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uint32_t buckets[32];
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};
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#endif // FLOW_HISTOGRAM_H
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