author | dholmes |
Tue, 09 Oct 2018 20:38:13 -0400 | |
changeset 52067 | 2e72562697bf |
parent 51647 | 11ad7d302a94 |
child 52077 | b6eaf7b7cd7f |
permissions | -rw-r--r-- |
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/* |
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* Copyright (c) 2018, Oracle and/or its affiliates. All rights reserved. |
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* Copyright (c) 2018, Google and/or its affiliates. All rights reserved. |
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
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* |
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* This code is free software; you can redistribute it and/or modify it |
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* under the terms of the GNU General Public License version 2 only, as |
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* published by the Free Software Foundation. |
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* |
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* This code is distributed in the hope that it will be useful, but WITHOUT |
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
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* version 2 for more details (a copy is included in the LICENSE file that |
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* accompanied this code). |
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* |
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* You should have received a copy of the GNU General Public License version |
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* 2 along with this work; if not, write to the Free Software Foundation, |
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
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* |
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* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA |
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* or visit www.oracle.com if you need additional information or have any |
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* questions. |
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* |
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*/ |
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#include "precompiled.hpp" |
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#include "runtime/handles.inline.hpp" |
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#include "runtime/orderAccess.hpp" |
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#include "runtime/sharedRuntime.hpp" |
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#include "runtime/threadHeapSampler.hpp" |
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// Cheap random number generator |
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uint64_t ThreadHeapSampler::_rnd; |
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// Default is 512kb. |
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int ThreadHeapSampler::_sampling_interval = 512 * 1024; |
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int ThreadHeapSampler::_enabled; |
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// Statics for the fast log |
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static const int FastLogNumBits = 10; |
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static const int FastLogMask = (1 << FastLogNumBits) - 1; |
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static double log_table[1<<FastLogNumBits]; // Constant |
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static bool log_table_initialized; |
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// Returns the next prng value. |
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// pRNG is: aX+b mod c with a = 0x5DEECE66D, b = 0xB, c = 1<<48 |
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// This is the lrand64 generator. |
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static uint64_t next_random(uint64_t rnd) { |
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const uint64_t PrngMult = 0x5DEECE66DLL; |
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const uint64_t PrngAdd = 0xB; |
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const uint64_t PrngModPower = 48; |
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const uint64_t PrngModMask = ((uint64_t)1 << PrngModPower) - 1; |
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//assert(IS_SAFE_SIZE_MUL(PrngMult, rnd), "Overflow on multiplication."); |
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//assert(IS_SAFE_SIZE_ADD(PrngMult * rnd, PrngAdd), "Overflow on addition."); |
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return (PrngMult * rnd + PrngAdd) & PrngModMask; |
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} |
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static double fast_log2(const double & d) { |
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assert(d>0, "bad value passed to assert"); |
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uint64_t x = 0; |
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assert(sizeof(d) == sizeof(x), |
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"double and uint64_t do not have the same size"); |
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x = *reinterpret_cast<const uint64_t*>(&d); |
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const uint32_t x_high = x >> 32; |
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assert(FastLogNumBits <= 20, "FastLogNumBits should be less than 20."); |
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const uint32_t y = x_high >> (20 - FastLogNumBits) & FastLogMask; |
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const int32_t exponent = ((x_high >> 20) & 0x7FF) - 1023; |
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return exponent + log_table[y]; |
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} |
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// Generates a geometric variable with the specified mean (512K by default). |
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// This is done by generating a random number between 0 and 1 and applying |
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// the inverse cumulative distribution function for an exponential. |
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// Specifically: Let m be the inverse of the sample interval, then |
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// the probability distribution function is m*exp(-mx) so the CDF is |
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// p = 1 - exp(-mx), so |
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// q = 1 - p = exp(-mx) |
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// log_e(q) = -mx |
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// -log_e(q)/m = x |
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// log_2(q) * (-log_e(2) * 1/m) = x |
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// In the code, q is actually in the range 1 to 2**26, hence the -26 below |
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void ThreadHeapSampler::pick_next_geometric_sample() { |
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_rnd = next_random(_rnd); |
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// Take the top 26 bits as the random number |
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// (This plus a 1<<58 sampling bound gives a max possible step of |
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// 5194297183973780480 bytes. In this case, |
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// for sample_parameter = 1<<19, max possible step is |
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// 9448372 bytes (24 bits). |
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const uint64_t PrngModPower = 48; // Number of bits in prng |
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// The uint32_t cast is to prevent a (hard-to-reproduce) NAN |
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// under piii debug for some binaries. |
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double q = static_cast<uint32_t>(_rnd >> (PrngModPower - 26)) + 1.0; |
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// Put the computed p-value through the CDF of a geometric. |
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// For faster performance (save ~1/20th exec time), replace |
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// min(0.0, FastLog2(q) - 26) by (Fastlog2(q) - 26.000705) |
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// The value 26.000705 is used rather than 26 to compensate |
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// for inaccuracies in FastLog2 which otherwise result in a |
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// negative answer. |
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double log_val = (fast_log2(q) - 26); |
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double result = |
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(0.0 < log_val ? 0.0 : log_val) * (-log(2.0) * (get_sampling_interval())) + 1; |
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assert(result > 0 && result < SIZE_MAX, "Result is not in an acceptable range."); |
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size_t interval = static_cast<size_t>(result); |
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_bytes_until_sample = interval; |
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} |
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void ThreadHeapSampler::pick_next_sample(size_t overflowed_bytes) { |
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// Explicitly test if the sampling interval is 0, return 0 to sample every |
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// allocation. |
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if (get_sampling_interval() == 0) { |
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_bytes_until_sample = 0; |
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return; |
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} |
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pick_next_geometric_sample(); |
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// Try to correct sample size by removing extra space from last allocation. |
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if (overflowed_bytes > 0 && _bytes_until_sample > overflowed_bytes) { |
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_bytes_until_sample -= overflowed_bytes; |
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} |
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} |
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void ThreadHeapSampler::check_for_sampling(oop obj, size_t allocation_size, size_t bytes_since_allocation) { |
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size_t total_allocated_bytes = bytes_since_allocation + allocation_size; |
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// If not yet time for a sample, skip it. |
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if (total_allocated_bytes < _bytes_until_sample) { |
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_bytes_until_sample -= total_allocated_bytes; |
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return; |
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} |
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JvmtiExport::sampled_object_alloc_event_collector(obj); |
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size_t overflow_bytes = total_allocated_bytes - _bytes_until_sample; |
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pick_next_sample(overflow_bytes); |
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} |
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void ThreadHeapSampler::init_log_table() { |
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MutexLockerEx mu(ThreadHeapSampler_lock, Mutex::_no_safepoint_check_flag); |
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if (log_table_initialized) { |
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return; |
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} |
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for (int i = 0; i < (1 << FastLogNumBits); i++) { |
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log_table[i] = (log(1.0 + static_cast<double>(i+0.5) / (1 << FastLogNumBits)) |
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/ log(2.0)); |
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} |
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log_table_initialized = true; |
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} |
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void ThreadHeapSampler::enable() { |
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// Done here to be done when things have settled. This adds a mutex lock but |
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// presumably, users won't be enabling and disabling all the time. |
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init_log_table(); |
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OrderAccess::release_store(&_enabled, 1); |
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} |
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int ThreadHeapSampler::enabled() { |
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return OrderAccess::load_acquire(&_enabled); |
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} |
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void ThreadHeapSampler::disable() { |
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OrderAccess::release_store(&_enabled, 0); |
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} |
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int ThreadHeapSampler::get_sampling_interval() { |
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return OrderAccess::load_acquire(&_sampling_interval); |
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} |
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void ThreadHeapSampler::set_sampling_interval(int sampling_interval) { |
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OrderAccess::release_store(&_sampling_interval, sampling_interval); |
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} |
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// Methods used in assertion mode to check if a collector is present or not at |
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// the moment of TLAB sampling, ie a slow allocation path. |
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bool ThreadHeapSampler::sampling_collector_present() const { |
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return _collectors_present > 0; |
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} |
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bool ThreadHeapSampler::remove_sampling_collector() { |
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assert(_collectors_present > 0, "Problem with collector counter."); |
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_collectors_present--; |
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return true; |
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} |
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bool ThreadHeapSampler::add_sampling_collector() { |
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_collectors_present++; |
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return true; |
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} |