7d3a0f0789
This patch contains two changes to the histogram implementation. It uses a simpler method to calculate the estimated mean (simply divide the estimated sum with the number of samples) and to make sure that there will always be values in the histogram, it start with taking a sample (when there are no samples) and then use the mask to decide if to sample or not. Signed-off-by: Amnon Heiman <amnon@cloudius-systems.com>
108 lines
2.8 KiB
C++
108 lines
2.8 KiB
C++
/*
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* Copyright 2015 Cloudius Systems
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*/
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/*
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* This file is part of Scylla.
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*
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* Scylla is free software: you can redistribute it and/or modify
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* it under the terms of the GNU Affero General Public License as published by
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* the Free Software Foundation, either version 3 of the License, or
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* (at your option) any later version.
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*
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* Scylla is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with Scylla. If not, see <http://www.gnu.org/licenses/>.
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*/
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#pragma once
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#include <boost/circular_buffer.hpp>
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#include "latency.hh"
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namespace utils {
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class ihistogram {
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public:
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// count holds all the events
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int64_t count;
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// total holds only the events we sample
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int64_t total;
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int64_t min;
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int64_t max;
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int64_t sum;
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double mean;
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double variance;
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int64_t sample_mask;
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boost::circular_buffer<int64_t> sample;
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ihistogram(size_t size = 1024, int64_t _sample_mask = 0x80)
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: count(0), total(0), min(0), max(0), sum(0), mean(0), variance(0),
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sample_mask(_sample_mask), sample(
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size) {
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}
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void mark(int64_t value) {
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if (total == 0 || value < min) {
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min = value;
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}
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if (total == 0 || value > max) {
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max = value;
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}
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if (total == 0) {
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mean = value;
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variance = 0;
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} else {
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double old_m = mean;
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double old_s = variance;
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mean = ((double)(sum + value)) / (total + 1);
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variance = old_s + ((value - old_m) * (value - mean));
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}
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sum += value;
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total++;
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count++;
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sample.push_back(value);
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}
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void mark(latency_counter& lc) {
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if (lc.is_start()) {
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mark(lc.stop().latency_in_nano());
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} else {
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count++;
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}
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}
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/**
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* Return true if the current event should be sample.
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* In the typical case, there is no need to use this method
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* Call set_latency, that would start a latency object if needed.
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*/
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bool should_sample() const {
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return total == 0 || (count & sample_mask);
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}
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/**
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* Set the latency according to the sample rate.
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*/
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ihistogram& set_latency(latency_counter& lc) {
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if (should_sample()) {
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lc.start();
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}
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return *this;
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}
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/**
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* Allow to use the histogram as a counter
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* Increment the total number of events without
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* sampling the value.
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*/
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ihistogram& inc() {
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count++;
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return *this;
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}
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};
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}
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