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// Copyright 2018 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef UI_LATENCY_HISTOGRAMS_H_
#define UI_LATENCY_HISTOGRAMS_H_
#include <array>
#include <memory>
#include "base/macros.h"
namespace ui {
// Used to communicate percentile results to clients.
// If entries in |values| are zero, that means there were no samples.
// A non-zero value implies samples were added since, even if those samples
// were zero, they would go into the [0,N) bucket and result in a non-zero
// estimate.
struct PercentileResults {
static constexpr double kPercentiles[] = {.50, .99};
static constexpr size_t kCount = arraysize(kPercentiles);
double values[kCount]{};
};
namespace frame_metrics {
// This is an interface different metrics will use to inject their ideal
// histogram implementations into the StreamAnalyzer.
class Histogram {
public:
Histogram() = default;
virtual ~Histogram() = default;
// Increases the bucket that contains |value| by |weight|.
virtual void AddSample(uint32_t value, uint32_t weight) = 0;
// Computes and returns the approximate percentiles based on the
// histogram distribution.
virtual PercentileResults ComputePercentiles() const = 0;
// Resets all buckets in the histogram to 0.
// Higher level logic may periodically reset the the counts after it
// gathers the percentiles in order to avoid overflow.
virtual void Reset() = 0;
private:
DISALLOW_COPY_AND_ASSIGN(Histogram);
};
// Ratio histogram, with a range of [0, 2^32) and most of it's precision
// just above kFixedPointMultiplier (i.e. a fixed point of 1).
class RatioHistogram : public Histogram {
public:
RatioHistogram();
~RatioHistogram() override;
void AddSample(uint32_t ratio, uint32_t weight) override;
PercentileResults ComputePercentiles() const override;
void Reset() override;
private:
static constexpr size_t kBucketCount = 111;
uint64_t total_samples_ = 0;
using BucketArray = std::array<uint32_t, kBucketCount>;
BucketArray buckets_{};
DISALLOW_COPY_AND_ASSIGN(RatioHistogram);
};
// A histogram of 98 buckets from 0 to 64 seconds with extra precision
// around common vsync boundaries.
class VSyncHistogram : public Histogram {
public:
VSyncHistogram();
~VSyncHistogram() override;
void AddSample(uint32_t microseconds, uint32_t weight) override;
PercentileResults ComputePercentiles() const override;
void Reset() override;
private:
static constexpr size_t kBucketCount = 98;
uint64_t total_samples_ = 0;
using BucketArray = std::array<uint32_t, kBucketCount>;
BucketArray buckets_{};
DISALLOW_COPY_AND_ASSIGN(VSyncHistogram);
};
// An interface that allows PercentileHelper to iterate through the
// bucket boundaries of the delegating histogram.
// This is an implemenation detail, but is exposed here for testing purposes.
struct BoundaryIterator {
virtual ~BoundaryIterator() = default;
virtual uint64_t Next() = 0;
};
// These expose the internal iterators, so they can be verified in tests.
std::unique_ptr<BoundaryIterator> CreateRatioIteratorForTesting();
std::unique_ptr<BoundaryIterator> CreateVSyncIteratorForTesting();
} // namespace frame_metrics
} // namespace ui
#endif // UI_LATENCY_HISTOGRAMS_H_
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