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/*
* Copyright (C) 2012 Apple Inc. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
* EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR
* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
* EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
* OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
#include "config.h"
#include "ExecutionCounter.h"
#include "CodeBlock.h"
#include "ExecutableAllocator.h"
#include <wtf/StringExtras.h>
namespace JSC {
ExecutionCounter::ExecutionCounter()
{
reset();
}
bool ExecutionCounter::checkIfThresholdCrossedAndSet(CodeBlock* codeBlock)
{
if (hasCrossedThreshold(codeBlock))
return true;
if (setThreshold(codeBlock))
return true;
return false;
}
void ExecutionCounter::setNewThreshold(int32_t threshold, CodeBlock* codeBlock)
{
reset();
m_activeThreshold = threshold;
setThreshold(codeBlock);
}
void ExecutionCounter::deferIndefinitely()
{
m_totalCount = 0;
m_activeThreshold = std::numeric_limits<int32_t>::max();
m_counter = std::numeric_limits<int32_t>::min();
}
double ExecutionCounter::applyMemoryUsageHeuristics(int32_t value, CodeBlock* codeBlock)
{
#if ENABLE(JIT)
double multiplier =
ExecutableAllocator::memoryPressureMultiplier(
codeBlock->predictedMachineCodeSize());
#else
// This code path will probably not be taken, but if it is, we fake it.
double multiplier = 1.0;
UNUSED_PARAM(codeBlock);
#endif
ASSERT(multiplier >= 1.0);
return multiplier * value;
}
int32_t ExecutionCounter::applyMemoryUsageHeuristicsAndConvertToInt(
int32_t value, CodeBlock* codeBlock)
{
double doubleResult = applyMemoryUsageHeuristics(value, codeBlock);
ASSERT(doubleResult >= 0);
if (doubleResult > std::numeric_limits<int32_t>::max())
return std::numeric_limits<int32_t>::max();
return static_cast<int32_t>(doubleResult);
}
bool ExecutionCounter::hasCrossedThreshold(CodeBlock* codeBlock) const
{
// This checks if the current count rounded up to the threshold we were targeting.
// For example, if we are using half of available executable memory and have
// m_activeThreshold = 1000, applyMemoryUsageHeuristics(m_activeThreshold) will be
// 2000, but we will pretend as if the threshold was crossed if we reach 2000 -
// 1000 / 2, or 1500. The reasoning here is that we want to avoid thrashing. If
// this method returns false, then the JIT's threshold for when it will again call
// into the slow path (which will call this method a second time) will be set
// according to the difference between the current count and the target count
// according to *current* memory usage. But by the time we call into this again, we
// may have JIT'ed more code, and so the target count will increase slightly. This
// may lead to a repeating pattern where the target count is slightly incremented,
// the JIT immediately matches that increase, calls into the slow path again, and
// again the target count is slightly incremented. Instead of having this vicious
// cycle, we declare victory a bit early if the difference between the current
// total and our target according to memory heuristics is small. Our definition of
// small is arbitrarily picked to be half of the original threshold (i.e.
// m_activeThreshold).
double modifiedThreshold = applyMemoryUsageHeuristics(m_activeThreshold, codeBlock);
return static_cast<double>(m_totalCount) + m_counter >=
modifiedThreshold - static_cast<double>(
std::min(m_activeThreshold, Options::maximumExecutionCountsBetweenCheckpoints())) / 2;
}
bool ExecutionCounter::setThreshold(CodeBlock* codeBlock)
{
if (m_activeThreshold == std::numeric_limits<int32_t>::max()) {
deferIndefinitely();
return false;
}
ASSERT(!hasCrossedThreshold(codeBlock));
// Compute the true total count.
double trueTotalCount = count();
// Correct the threshold for current memory usage.
double threshold = applyMemoryUsageHeuristics(m_activeThreshold, codeBlock);
// Threshold must be non-negative and not NaN.
ASSERT(threshold >= 0);
// Adjust the threshold according to the number of executions we have already
// seen. This shouldn't go negative, but it might, because of round-off errors.
threshold -= trueTotalCount;
if (threshold <= 0) {
m_counter = 0;
m_totalCount = trueTotalCount;
return true;
}
threshold = clippedThreshold(codeBlock->globalObject(), threshold);
m_counter = static_cast<int32_t>(-threshold);
m_totalCount = trueTotalCount + threshold;
return false;
}
void ExecutionCounter::reset()
{
m_counter = 0;
m_totalCount = 0;
m_activeThreshold = 0;
}
void ExecutionCounter::dump(PrintStream& out) const
{
out.printf("%lf/%lf, %d", count(), static_cast<double>(m_activeThreshold), m_counter);
}
} // namespace JSC
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