bytecode/ExecutionCounter.cpp

   1 /*
   2  * Copyright (C) 2012 Apple Inc. All rights reserved.
   3  *
   4  * Redistribution and use in source and binary forms, with or without
   5  * modification, are permitted provided that the following conditions
   6  * are met:
   7  * 1. Redistributions of source code must retain the above copyright
   8  *    notice, this list of conditions and the following disclaimer.
   9  * 2. Redistributions in binary form must reproduce the above copyright
  10  *    notice, this list of conditions and the following disclaimer in the
  11  *    documentation and/or other materials provided with the distribution.
  12  *
  13  * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
  14  * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  15  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
  16  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
  17  * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
  18  * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
  19  * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
  20  * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
  21  * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  22  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  23  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  24  */
  25
  26 #include "config.h"
  27 #include "ExecutionCounter.h"
  28
  29 #include "CodeBlock.h"
  30 #include "ExecutableAllocator.h"
  31 #include <wtf/StringExtras.h>
  32
  33 namespace JSC {
  34
  35 ExecutionCounter::ExecutionCounter()
  36 {
  37     reset();
  38 }
  39
  40 bool ExecutionCounter::checkIfThresholdCrossedAndSet(CodeBlock* codeBlock)
  41 {
  42     if (hasCrossedThreshold(codeBlock))
  43         return true;
  44
  45     if (setThreshold(codeBlock))
  46         return true;
  47
  48     return false;
  49 }
  50
  51 void ExecutionCounter::setNewThreshold(int32_t threshold, CodeBlock* codeBlock)
  52 {
  53     reset();
  54     m_activeThreshold = threshold;
  55     setThreshold(codeBlock);
  56 }
  57
  58 void ExecutionCounter::deferIndefinitely()
  59 {
  60     m_totalCount = 0;
  61     m_activeThreshold = std::numeric_limits<int32_t>::max();
  62     m_counter = std::numeric_limits<int32_t>::min();
  63 }
  64
  65 double ExecutionCounter::applyMemoryUsageHeuristics(int32_t value, CodeBlock* codeBlock)
  66 {
  67 #if ENABLE(JIT)
  68     double multiplier =
  69         ExecutableAllocator::memoryPressureMultiplier(
  70             codeBlock->predictedMachineCodeSize());
  71 #else
  72     // This code path will probably not be taken, but if it is, we fake it.
  73     double multiplier = 1.0;
  74     UNUSED_PARAM(codeBlock);
  75 #endif
  76     ASSERT(multiplier >= 1.0);
  77     return multiplier * value;
  78 }
  79
  80 int32_t ExecutionCounter::applyMemoryUsageHeuristicsAndConvertToInt(
  81     int32_t value, CodeBlock* codeBlock)
  82 {
  83     double doubleResult = applyMemoryUsageHeuristics(value, codeBlock);
  84
  85     ASSERT(doubleResult >= 0);
  86
  87     if (doubleResult > std::numeric_limits<int32_t>::max())
  88         return std::numeric_limits<int32_t>::max();
  89
  90     return static_cast<int32_t>(doubleResult);
  91 }
  92
  93 bool ExecutionCounter::hasCrossedThreshold(CodeBlock* codeBlock) const
  94 {
  95     // This checks if the current count rounded up to the threshold we were targeting.
  96     // For example, if we are using half of available executable memory and have
  97     // m_activeThreshold = 1000, applyMemoryUsageHeuristics(m_activeThreshold) will be
  98     // 2000, but we will pretend as if the threshold was crossed if we reach 2000 -
  99     // 1000 / 2, or 1500. The reasoning here is that we want to avoid thrashing. If
 100     // this method returns false, then the JIT's threshold for when it will again call
 101     // into the slow path (which will call this method a second time) will be set
 102     // according to the difference between the current count and the target count
 103     // according to *current* memory usage. But by the time we call into this again, we
 104     // may have JIT'ed more code, and so the target count will increase slightly. This
 105     // may lead to a repeating pattern where the target count is slightly incremented,
 106     // the JIT immediately matches that increase, calls into the slow path again, and
 107     // again the target count is slightly incremented. Instead of having this vicious
 108     // cycle, we declare victory a bit early if the difference between the current
 109     // total and our target according to memory heuristics is small. Our definition of
 110     // small is arbitrarily picked to be half of the original threshold (i.e.
 111     // m_activeThreshold).
 112
 113     double modifiedThreshold = applyMemoryUsageHeuristics(m_activeThreshold, codeBlock);
 114
 115     return static_cast<double>(m_totalCount) + m_counter >=
 116         modifiedThreshold - static_cast<double>(
 117             std::min(m_activeThreshold, Options::maximumExecutionCountsBetweenCheckpoints())) / 2;
 118 }
 119
 120 bool ExecutionCounter::setThreshold(CodeBlock* codeBlock)
 121 {
 122     if (m_activeThreshold == std::numeric_limits<int32_t>::max()) {
 123         deferIndefinitely();
 124         return false;
 125     }
 126
 127     ASSERT(!hasCrossedThreshold(codeBlock));
 128
 129     // Compute the true total count.
 130     double trueTotalCount = count();
 131
 132     // Correct the threshold for current memory usage.
 133     double threshold = applyMemoryUsageHeuristics(m_activeThreshold, codeBlock);
 134
 135     // Threshold must be non-negative and not NaN.
 136     ASSERT(threshold >= 0);
 137
 138     // Adjust the threshold according to the number of executions we have already
 139     // seen. This shouldn't go negative, but it might, because of round-off errors.
 140     threshold -= trueTotalCount;
 141
 142     if (threshold <= 0) {
 143         m_counter = 0;
 144         m_totalCount = trueTotalCount;
 145         return true;
 146     }
 147
 148     threshold = clippedThreshold(codeBlock->globalObject(), threshold);
 149
 150     m_counter = static_cast<int32_t>(-threshold);
 151
 152     m_totalCount = trueTotalCount + threshold;
 153
 154     return false;
 155 }
 156
 157 void ExecutionCounter::reset()
 158 {
 159     m_counter = 0;
 160     m_totalCount = 0;
 161     m_activeThreshold = 0;
 162 }
 163
 164 void ExecutionCounter::dump(PrintStream& out) const
 165 {
 166     out.printf("%lf/%lf, %d", count(), static_cast<double>(m_activeThreshold), m_counter);
 167 }
 168
 169 } // namespace JSC
 170