1 /*
2  * Copyright (C) 2020 The Android Open Source Project
3  *
4  * Licensed under the Apache License, Version 2.0 (the "License");
5  * you may not use this file except in compliance with the License.
6  * You may obtain a copy of the License at
7  *
8  *      http://www.apache.org/licenses/LICENSE-2.0
9  *
10  * Unless required by applicable law or agreed to in writing, software
11  * distributed under the License is distributed on an "AS IS" BASIS,
12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13  * See the License for the specific language governing permissions and
14  * limitations under the License.
15  */
16 
17 #include "src/profiling/memory/sampler.h"
18 
19 namespace perfetto {
20 namespace profiling {
21 
22 namespace {
23 
24 // If the probability of getting less than one sample is less than this,
25 // sidestep the sampler and treat the allocation as a sample.
26 constexpr double kPassthroughError = 0.01;
27 
28 }  // namespace
29 
GetPassthroughThreshold(uint64_t interval)30 uint64_t GetPassthroughThreshold(uint64_t interval) {
31   if (interval <= 1)
32     return interval;
33   // (1 - 1 / interval)^x = kPassthroughError
34   // x = log_(1 - 1/interval)(kPassthroughError)
35   return 1 + uint64_t(log(kPassthroughError) / log(1.0 - 1 / double(interval)));
36 }
37 
GetGlobalRandomEngineLocked()38 std::default_random_engine& GetGlobalRandomEngineLocked() {
39   static std::default_random_engine engine;
40   return engine;
41 }
42 
SetSamplingInterval(uint64_t sampling_interval)43 void Sampler::SetSamplingInterval(uint64_t sampling_interval) {
44   sampling_interval_ = sampling_interval;
45   passthrough_threshold_ = GetPassthroughThreshold(sampling_interval_);
46   sampling_rate_ = 1.0 / static_cast<double>(sampling_interval_);
47   interval_to_next_sample_ = NextSampleInterval();
48 }
49 
50 }  // namespace profiling
51 }  // namespace perfetto
52