1 /* 2 * Copyright (c) 2018, Oracle and/or its affiliates. All rights reserved. 3 * Copyright (c) 2018, Google and/or its affiliates. All rights reserved. 4 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 5 * 6 * This code is free software; you can redistribute it and/or modify it 7 * under the terms of the GNU General Public License version 2 only, as 8 * published by the Free Software Foundation. 9 * 10 * This code is distributed in the hope that it will be useful, but WITHOUT 11 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 12 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 13 * version 2 for more details (a copy is included in the LICENSE file that 14 * accompanied this code). 15 * 16 * You should have received a copy of the GNU General Public License version 17 * 2 along with this work; if not, write to the Free Software Foundation, 18 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 19 * 20 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 21 * or visit www.oracle.com if you need additional information or have any 22 * questions. 23 * 24 */ 25 26 #include "precompiled.hpp" 27 #include "runtime/handles.inline.hpp" 28 #include "runtime/orderAccess.hpp" 29 #include "runtime/sharedRuntime.hpp" 30 #include "runtime/threadHeapSampler.hpp" 31 32 // Cheap random number generator 33 uint64_t ThreadHeapSampler::_rnd; 34 // Default is 512kb. 35 int ThreadHeapSampler::_sampling_interval = 512 * 1024; 36 int ThreadHeapSampler::_enabled; 37 38 // Statics for the fast log 39 static const int FastLogNumBits = 10; 40 static const int FastLogMask = (1 << FastLogNumBits) - 1; 41 static double log_table[1<<FastLogNumBits]; // Constant 42 static bool log_table_initialized; 43 44 // Returns the next prng value. 45 // pRNG is: aX+b mod c with a = 0x5DEECE66D, b = 0xB, c = 1<<48 46 // This is the lrand64 generator. 47 static uint64_t next_random(uint64_t rnd) { 48 const uint64_t PrngMult = 0x5DEECE66DLL; 49 const uint64_t PrngAdd = 0xB; 50 const uint64_t PrngModPower = 48; 51 const uint64_t PrngModMask = ((uint64_t)1 << PrngModPower) - 1; 52 //assert(IS_SAFE_SIZE_MUL(PrngMult, rnd), "Overflow on multiplication."); 53 //assert(IS_SAFE_SIZE_ADD(PrngMult * rnd, PrngAdd), "Overflow on addition."); 54 return (PrngMult * rnd + PrngAdd) & PrngModMask; 55 } 56 57 static double fast_log2(const double & d) { 58 assert(d>0, "bad value passed to assert"); 59 uint64_t x = 0; 60 assert(sizeof(d) == sizeof(x), 61 "double and uint64_t do not have the same size"); 62 x = *reinterpret_cast<const uint64_t*>(&d); 63 const uint32_t x_high = x >> 32; 64 assert(FastLogNumBits <= 20, "FastLogNumBits should be less than 20."); 65 const uint32_t y = x_high >> (20 - FastLogNumBits) & FastLogMask; 66 const int32_t exponent = ((x_high >> 20) & 0x7FF) - 1023; 67 return exponent + log_table[y]; 68 } 69 70 // Generates a geometric variable with the specified mean (512K by default). 71 // This is done by generating a random number between 0 and 1 and applying 72 // the inverse cumulative distribution function for an exponential. 73 // Specifically: Let m be the inverse of the sample interval, then 74 // the probability distribution function is m*exp(-mx) so the CDF is 75 // p = 1 - exp(-mx), so 76 // q = 1 - p = exp(-mx) 77 // log_e(q) = -mx 78 // -log_e(q)/m = x 79 // log_2(q) * (-log_e(2) * 1/m) = x 80 // In the code, q is actually in the range 1 to 2**26, hence the -26 below 81 void ThreadHeapSampler::pick_next_geometric_sample() { 82 _rnd = next_random(_rnd); 83 // Take the top 26 bits as the random number 84 // (This plus a 1<<58 sampling bound gives a max possible step of 85 // 5194297183973780480 bytes. In this case, 86 // for sample_parameter = 1<<19, max possible step is 87 // 9448372 bytes (24 bits). 88 const uint64_t PrngModPower = 48; // Number of bits in prng 89 // The uint32_t cast is to prevent a (hard-to-reproduce) NAN 90 // under piii debug for some binaries. 91 double q = static_cast<uint32_t>(_rnd >> (PrngModPower - 26)) + 1.0; 92 // Put the computed p-value through the CDF of a geometric. 93 // For faster performance (save ~1/20th exec time), replace 94 // min(0.0, FastLog2(q) - 26) by (Fastlog2(q) - 26.000705) 95 // The value 26.000705 is used rather than 26 to compensate 96 // for inaccuracies in FastLog2 which otherwise result in a 97 // negative answer. 98 double log_val = (fast_log2(q) - 26); 99 double result = 100 (0.0 < log_val ? 0.0 : log_val) * (-log(2.0) * (get_sampling_interval())) + 1; 101 assert(result > 0 && result < SIZE_MAX, "Result is not in an acceptable range."); 102 size_t interval = static_cast<size_t>(result); 103 _bytes_until_sample = interval; 104 } 105 106 void ThreadHeapSampler::pick_next_sample(size_t overflowed_bytes) { 107 // Explicitly test if the sampling interval is 0, return 0 to sample every 108 // allocation. 109 if (get_sampling_interval() == 0) { 110 _bytes_until_sample = 0; 111 return; 112 } 113 114 pick_next_geometric_sample(); 115 116 // Try to correct sample size by removing extra space from last allocation. 117 if (overflowed_bytes > 0 && _bytes_until_sample > overflowed_bytes) { 118 _bytes_until_sample -= overflowed_bytes; 119 } 120 } 121 122 void ThreadHeapSampler::check_for_sampling(oop obj, size_t allocation_size, size_t bytes_since_allocation) { 123 size_t total_allocated_bytes = bytes_since_allocation + allocation_size; 124 125 // If not yet time for a sample, skip it. 126 if (total_allocated_bytes < _bytes_until_sample) { 127 _bytes_until_sample -= total_allocated_bytes; 128 return; 129 } 130 131 JvmtiExport::sampled_object_alloc_event_collector(obj); 132 133 size_t overflow_bytes = total_allocated_bytes - _bytes_until_sample; 134 pick_next_sample(overflow_bytes); 135 } 136 137 void ThreadHeapSampler::init_log_table() { 138 MutexLockerEx mu(ThreadHeapSampler_lock, Mutex::_no_safepoint_check_flag); 139 140 if (log_table_initialized) { 141 return; 142 } 143 144 for (int i = 0; i < (1 << FastLogNumBits); i++) { 145 log_table[i] = (log(1.0 + static_cast<double>(i+0.5) / (1 << FastLogNumBits)) 146 / log(2.0)); 147 } 148 149 log_table_initialized = true; 150 } 151 152 void ThreadHeapSampler::enable() { 153 // Done here to be done when things have settled. This adds a mutex lock but 154 // presumably, users won't be enabling and disabling all the time. 155 init_log_table(); 156 OrderAccess::release_store(&_enabled, 1); 157 } 158 159 int ThreadHeapSampler::enabled() { 160 return OrderAccess::load_acquire(&_enabled); 161 } 162 163 void ThreadHeapSampler::disable() { 164 OrderAccess::release_store(&_enabled, 0); 165 } 166 167 int ThreadHeapSampler::get_sampling_interval() { 168 return OrderAccess::load_acquire(&_sampling_interval); 169 } 170 171 void ThreadHeapSampler::set_sampling_interval(int sampling_interval) { 172 OrderAccess::release_store(&_sampling_interval, sampling_interval); 173 } 174 175 // Methods used in assertion mode to check if a collector is present or not at 176 // the moment of TLAB sampling, ie a slow allocation path. 177 bool ThreadHeapSampler::sampling_collector_present() const { 178 return _collectors_present > 0; 179 } 180 181 bool ThreadHeapSampler::remove_sampling_collector() { 182 assert(_collectors_present > 0, "Problem with collector counter."); 183 _collectors_present--; 184 return true; 185 } 186 187 bool ThreadHeapSampler::add_sampling_collector() { 188 _collectors_present++; 189 return true; 190 }