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Scavenger.cpp
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Scavenger.cpp
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/*******************************************************************************
* Copyright (c) 1991, 2021 IBM Corp. and others
*
* This program and the accompanying materials are made available under
* the terms of the Eclipse Public License 2.0 which accompanies this
* distribution and is available at https://www.eclipse.org/legal/epl-2.0/
* or the Apache License, Version 2.0 which accompanies this distribution and
* is available at https://www.apache.org/licenses/LICENSE-2.0.
*
* This Source Code may also be made available under the following
* Secondary Licenses when the conditions for such availability set
* forth in the Eclipse Public License, v. 2.0 are satisfied: GNU
* General Public License, version 2 with the GNU Classpath
* Exception [1] and GNU General Public License, version 2 with the
* OpenJDK Assembly Exception [2].
*
* [1] https://www.gnu.org/software/classpath/license.html
* [2] http://openjdk.java.net/legal/assembly-exception.html
*
* SPDX-License-Identifier: EPL-2.0 OR Apache-2.0 OR GPL-2.0 WITH Classpath-exception-2.0 OR LicenseRef-GPL-2.0 WITH Assembly-exception
*******************************************************************************/
#if 0
#define OMR_SCAVENGER_DEBUG
#define OMR_SCAVENGER_TRACE
#define OMR_SCAVENGER_TRACE_REMEMBERED_SET
#define OMR_SCAVENGER_TRACE_BACKOUT
#define OMR_SCAVENGER_TRACE_COPY
#define OMR_SCAVENGER_TRACK_COPY_DISTANCE
#endif
#include <math.h>
#include "omrcfg.h"
#include "omrcomp.h"
#include "omrmodroncore.h"
#include "mmomrhook.h"
#include "mmomrhook_internal.h"
#include "modronapicore.hpp"
#include "modronbase.h"
#include "modronopt.h"
#include "ModronAssertions.h"
#include "omr.h"
#include "thread_api.h"
#if defined(OMR_GC_MODRON_SCAVENGER)
#include "AllocateDescription.hpp"
#include "AtomicOperations.hpp"
#include "CollectionStatisticsStandard.hpp"
#include "CollectorLanguageInterface.hpp"
#include "ConcurrentScavengeTask.hpp"
#include "ConfigurationStandard.hpp"
#include "CycleState.hpp"
#include "EnvironmentBase.hpp"
#include "EnvironmentStandard.hpp"
#include "ForwardedHeader.hpp"
#include "IndexableObjectScanner.hpp"
#include "Heap.hpp"
#include "HeapRegionDescriptorStandard.hpp"
#include "HeapRegionIterator.hpp"
#include "HeapRegionManager.hpp"
#include "HeapStats.hpp"
#include "MemoryPool.hpp"
#include "MemorySpace.hpp"
#include "MemorySubSpace.hpp"
#include "MemorySubSpaceRegionIterator.hpp"
#include "MemorySubSpaceRegionIteratorStandard.hpp"
#include "MemorySubSpaceSemiSpace.hpp"
#include "ObjectAllocationInterface.hpp"
#include "ObjectHeapIteratorAddressOrderedList.hpp"
#include "ObjectModel.hpp"
#include "ObjectScanner.hpp"
#include "OMRVMInterface.hpp"
#include "OMRVMThreadListIterator.hpp"
#include "ParallelDispatcher.hpp"
#include "ParallelScavengeTask.hpp"
#include "PhysicalSubArena.hpp"
#include "RSOverflow.hpp"
#include "Scavenger.hpp"
#include "ScavengerBackOutScanner.hpp"
#include "ScavengerRootScanner.hpp"
#include "ScavengerStats.hpp"
#include "SlotObject.hpp"
#include "SublistFragment.hpp"
#include "SublistIterator.hpp"
#include "SublistPool.hpp"
#include "SublistPuddle.hpp"
#include "SublistSlotIterator.hpp"
#if defined(OMR_VALGRIND_MEMCHECK)
#include "MemcheckWrapper.hpp"
#endif /* defined(OMR_VALGRIND_MEMCHECK) */
/* OMRTODO temporary workaround to allow both ut_j9mm.h and ut_omrmm.h to be included.
* Dependency on ut_j9mm.h should be removed in the future.
*/
#undef UT_MODULE_LOADED
#undef UT_MODULE_UNLOADED
#include "ut_omrmm.h"
#define INITIAL_FREE_HISTORY_WEIGHT ((float)0.8)
#define TENURE_BYTES_HISTORY_WEIGHT ((float)0.9)
#define FLIP_TENURE_LARGE_SCAN 4
#define FLIP_TENURE_LARGE_SCAN_DEFERRED 5
/* If scavenger dynamicBreadthFirstScanOrdering and alwaysDepthCopyFirstOffset is enabled, always copy the first offset of each object after the object itself is copied */
#define DEFAULT_HOT_FIELD_OFFSET 1
/* VM Design 1774: Ideally we would pull these cache line values from the port library but this will suffice for
* a quick implementation
*/
#if defined(AIXPPC) || defined(LINUXPPC)
#define CACHE_LINE_SIZE 128
#elif defined(J9ZOS390) || (defined(LINUX) && defined(S390))
#define CACHE_LINE_SIZE 256
#else
#define CACHE_LINE_SIZE 64
#endif
/* create macros to interpret the hot field descriptor */
#define HOTFIELD_SHOULD_ALIGN(descriptor) (0x1 == (0x1 & (descriptor)))
#define HOTFIELD_ALIGNMENT_BIAS(descriptor, heapObjectAlignment) (((descriptor) >> 1) * (heapObjectAlignment))
extern "C" {
uintptr_t allocateMemoryForSublistFragment(void *vmThreadRawPtr, J9VMGC_SublistFragment *fragmentPrimitive);
#if defined(OMR_GC_MODRON_CONCURRENT_MARK)
void oldToOldReferenceCreated(MM_EnvironmentBase *env, omrobjectptr_t objectPtr);
#endif /* OMR_GC_MODRON_CONCURRENT_MARK */
}
uintptr_t
MM_Scavenger::getVMStateID()
{
return OMRVMSTATE_GC_COLLECTOR_SCAVENGER;
}
void
MM_Scavenger::hookGlobalCollectionStart(J9HookInterface** hook, uintptr_t eventNum, void* eventData, void* userData)
{
MM_GlobalGCStartEvent *event = (MM_GlobalGCStartEvent *)eventData;
MM_EnvironmentBase *env = MM_EnvironmentBase::getEnvironment(event->currentThread);
((MM_Scavenger *)userData)->globalCollectionStart(env);
}
void
MM_Scavenger::hookGlobalCollectionComplete(J9HookInterface** hook, uintptr_t eventNum, void* eventData, void* userData)
{
MM_GlobalGCEndEvent *event = (MM_GlobalGCEndEvent *)eventData;
MM_EnvironmentBase *env = MM_EnvironmentBase::getEnvironment(event->currentThread);
((MM_Scavenger *)userData)->globalCollectionComplete(env);
}
/**
* Request to create sweepPoolState class for pool
* @param memoryPool memory pool to attach sweep state to
* @return pointer to created class
*/
void *
MM_Scavenger::createSweepPoolState(MM_EnvironmentBase *env, MM_MemoryPool *memoryPool)
{
Assert_MM_unreachable();
return NULL;
}
/**
* Request to destroy sweepPoolState class for pool
* @param sweepPoolState class to destroy
*/
void
MM_Scavenger::deleteSweepPoolState(MM_EnvironmentBase *env, void *sweepPoolState)
{
Assert_MM_unreachable();
}
/**
* Create a new instance of the receiver.
* @return a new instance of the receiver or NULL on failure.
*/
MM_Scavenger *
MM_Scavenger::newInstance(MM_EnvironmentStandard *env, MM_HeapRegionManager *regionManager)
{
MM_Scavenger *scavenger;
scavenger = (MM_Scavenger *)env->getForge()->allocate(sizeof(MM_Scavenger), OMR::GC::AllocationCategory::FIXED, OMR_GET_CALLSITE());
if (scavenger) {
new(scavenger) MM_Scavenger(env, regionManager);
if (!scavenger->initialize(env)) {
scavenger->kill(env);
scavenger = NULL;
}
}
return scavenger;
}
/**
* Destroy and free all resources associated to the receiver.
*/
void
MM_Scavenger::kill(MM_EnvironmentBase *env)
{
MM_EnvironmentStandard *envStandard = MM_EnvironmentStandard::getEnvironment(env);
tearDown(envStandard);
env->getForge()->free(this);
}
/**
* Initialization
*/
bool
MM_Scavenger::initialize(MM_EnvironmentBase *env)
{
J9HookInterface** mmOmrHooks = J9_HOOK_INTERFACE(_extensions->omrHookInterface);
/* Register hook for global GC end. */
(*mmOmrHooks)->J9HookRegisterWithCallSite(mmOmrHooks, J9HOOK_MM_OMR_GLOBAL_GC_START, hookGlobalCollectionStart, OMR_GET_CALLSITE(), (void *)this);
(*mmOmrHooks)->J9HookRegisterWithCallSite(mmOmrHooks, J9HOOK_MM_OMR_GLOBAL_GC_END, hookGlobalCollectionComplete, OMR_GET_CALLSITE(), (void *)this);
/* initialize the global scavenger gcCount */
_extensions->scavengerStats._gcCount = 0;
if (!_scavengeCacheFreeList.initialize(env, NULL)) {
return false;
}
if (!_scavengeCacheScanList.initialize(env, &_cachedEntryCount)) {
return false;
}
if (omrthread_monitor_init_with_name(&_scanCacheMonitor, 0, "MM_Scavenger::scanCacheMonitor")) {
return false;
}
/* do not spin when acquiring monitor to notify blocking thread about new work */
((J9ThreadAbstractMonitor *)_scanCacheMonitor)->flags &= ~J9THREAD_MONITOR_TRY_ENTER_SPIN;
if (omrthread_monitor_init_with_name(&_freeCacheMonitor, 0, "MM_Scavenger::freeCacheMonitor")) {
return false;
}
/* No thread can use more than _cachesPerThread cache entries at 1 time (flip, tenure, scan, large, possibly deferred)
* So long as (N * _cachesPerThread) cache entries exist,the head of the scan list
* will contain a valid entry. We set the appropriate number of caches per thread here */
switch (_extensions->scavengerScanOrdering) {
case MM_GCExtensionsBase::OMR_GC_SCAVENGER_SCANORDERING_BREADTH_FIRST:
case MM_GCExtensionsBase::OMR_GC_SCAVENGER_SCANORDERING_DYNAMIC_BREADTH_FIRST:
_cachesPerThread = FLIP_TENURE_LARGE_SCAN;
break;
case MM_GCExtensionsBase::OMR_GC_SCAVENGER_SCANORDERING_HIERARCHICAL:
/* deferred cache is only needed for hierarchical scanning */
_cachesPerThread = FLIP_TENURE_LARGE_SCAN_DEFERRED;
break;
default:
Assert_MM_unreachable();
break;
}
/**
*incrementNewSpaceSize =
* Xmnx <= 32MB ---> Xmnx
* 32MB < Xmnx < 4GB ---> MAX(Xmnx/16, 32MB)
* Xmnx >= 4GB ---> 256MB
*/
uintptr_t incrementNewSpaceSize = OMR_MAX(_extensions->maxNewSpaceSize/16, 32*1024*1024);
incrementNewSpaceSize = OMR_MIN(incrementNewSpaceSize, _extensions->maxNewSpaceSize);
incrementNewSpaceSize = OMR_MIN(incrementNewSpaceSize, 256*1024*1024);
uintptr_t incrementCacheCount = calculateMaxCacheCount(incrementNewSpaceSize);
uintptr_t totalActiveCacheCount = calculateMaxCacheCount(_extensions->heap->getActiveMemorySize(MEMORY_TYPE_NEW));
if (0 == totalActiveCacheCount) {
totalActiveCacheCount += 1;
}
if (!_scavengeCacheFreeList.resizeCacheEntries(env, totalActiveCacheCount, incrementCacheCount)) {
return false;
}
_cacheLineAlignment = CACHE_LINE_SIZE;
#if defined(OMR_GC_CONCURRENT_SCAVENGER)
if (_extensions->concurrentScavenger) {
if (!_mainGCThread.initialize(this, true, true, true)) {
return false;
}
}
#endif /* OMR_GC_CONCURRENT_SCAVENGER */
if (!_delegate.initialize(env)) {
return false;
}
return true;
}
void
MM_Scavenger::tearDown(MM_EnvironmentBase *env)
{
_delegate.tearDown(env);
_scavengeCacheFreeList.tearDown(env);
_scavengeCacheScanList.tearDown(env);
if (NULL != _scanCacheMonitor) {
omrthread_monitor_destroy(_scanCacheMonitor);
_scanCacheMonitor = NULL;
}
if (NULL != _freeCacheMonitor) {
omrthread_monitor_destroy(_freeCacheMonitor);
_freeCacheMonitor = NULL;
}
J9HookInterface** mmOmrHooks = J9_HOOK_INTERFACE(_extensions->omrHookInterface);
/* Unregister hook for global GC end. */
(*mmOmrHooks)->J9HookUnregister(mmOmrHooks, J9HOOK_MM_OMR_GLOBAL_GC_START, hookGlobalCollectionStart, (void *)this);
(*mmOmrHooks)->J9HookUnregister(mmOmrHooks, J9HOOK_MM_OMR_GLOBAL_GC_END, hookGlobalCollectionComplete, (void *)this);
}
/**
* Perform any collector initialization particular to the concurrent collector.
*/
bool
MM_Scavenger::collectorStartup(MM_GCExtensionsBase* extensions)
{
#if defined(OMR_GC_CONCURRENT_SCAVENGER)
if (_extensions->concurrentScavenger) {
if (!_mainGCThread.startup()) {
return false;
}
}
#endif /* OMR_GC_CONCURRENT_SCAVENGER */
return true;
}
/**
* Perform any collector shutdown particular to the concurrent collector.
* Currently this just involves stopping the concurrent background helper threads.
*/
void
MM_Scavenger::collectorShutdown(MM_GCExtensionsBase* extensions)
{
#if defined(OMR_GC_CONCURRENT_SCAVENGER)
if (_extensions->concurrentScavenger) {
_mainGCThread.shutdown();
}
#endif /* OMR_GC_CONCURRENT_SCAVENGER */
}
/****************************************
* Initialization routines
****************************************
*/
void
MM_Scavenger::setupForGC(MM_EnvironmentBase *env)
{
}
void
MM_Scavenger::mainSetupForGC(MM_EnvironmentStandard *env)
{
/* Make sure the backout state is cleared */
setBackOutFlag(env, backOutFlagCleared);
_rescanThreadsForRememberedObjects = false;
_doneIndex = 0;
restoreMainThreadTenureTLHRemainders(env);
/* Reinitialize the copy scan caches */
Assert_MM_true(_scavengeCacheFreeList.areAllCachesReturned());
Assert_MM_true(0 == _cachedEntryCount);
_extensions->copyScanRatio.reset(env, true);
/* Cache heap ranges for fast "valid object" checks (this can change in an expanding heap situation, so we refetch every cycle) */
_heapBase = _extensions->heap->getHeapBase();
_heapTop = _extensions->heap->getHeapTop();
/* ensure heap base is aligned to region size */
uintptr_t regionSize = _extensions->heap->getHeapRegionManager()->getRegionSize();
Assert_MM_true((0 != regionSize) && (0 == ((uintptr_t)_heapBase % regionSize)));
/* Clear the cycle gc statistics. Increment level stats will be cleared just prior to increment start. */
clearCycleGCStats(env);
/* invoke language-specific interface callback */
_delegate.mainSetupForGC(env);
/* Allow expansion in the tenure area on failed promotions (but no resizing on the semispace) */
_expandTenureOnFailedAllocate = true;
_activeSubSpace = (MM_MemorySubSpaceSemiSpace *)(env->_cycleState->_activeSubSpace);
_cachedSemiSpaceResizableFlag = _activeSubSpace->setResizable(false);
/* Reset the minimum failure sizes */
_minTenureFailureSize = UDATA_MAX;
_minSemiSpaceFailureSize = UDATA_MAX;
/* Find tenure memory sub spaces for collection ( allocate and survivor are context specific) */
/* Find the allocate, survivor and tenure memory sub spaces for collection */
/* Evacuate range for GC is what allocate space is for allocation */
_evacuateMemorySubSpace = _activeSubSpace->getMemorySubSpaceAllocate();
_survivorMemorySubSpace = _activeSubSpace->getMemorySubSpaceSurvivor();
_tenureMemorySubSpace = _activeSubSpace->getTenureMemorySubSpace();
/* Accumulate pre-scavenge allocation statistics */
MM_HeapStats heapStatsSemiSpace;
MM_HeapStats heapStatsTenureSpace;
MM_ScavengerStats* scavengerStats = &_extensions->scavengerStats;
_activeSubSpace->mergeHeapStats(&heapStatsSemiSpace);
_tenureMemorySubSpace->mergeHeapStats(&heapStatsTenureSpace);
scavengerStats->_tenureSpaceAllocBytesAcumulation += heapStatsTenureSpace._allocBytes;
scavengerStats->_semiSpaceAllocBytesAcumulation += heapStatsSemiSpace._allocBytes;
/* Check if scvTenureAdaptiveTenureAge has not been initialized or forced (by cmdline option) */
if (0 == _extensions->scvTenureAdaptiveTenureAge) {
/* With larger initial Nursery sizes, we'll reduce initial tenure age, to help promote peristant object sooner. */
_extensions->scvTenureAdaptiveTenureAge = OMR_OBJECT_HEADER_AGE_DEFAULT;
uintptr_t tenureAgeAdjustement = MM_Math::floorLog2(_extensions->heap->getActiveMemorySize(MEMORY_TYPE_NEW) / MINIMUM_NEW_SPACE_SIZE);
if (tenureAgeAdjustement < _extensions->scvTenureAdaptiveTenureAge) {
_extensions->scvTenureAdaptiveTenureAge -= tenureAgeAdjustement;
} else {
_extensions->scvTenureAdaptiveTenureAge = 1;
}
}
/* Record the tenure mask */
_tenureMask = calculateTenureMask();
_activeSubSpace->mainSetupForGC(env);
_activeSubSpace->cacheRanges(_evacuateMemorySubSpace, &_evacuateSpaceBase, &_evacuateSpaceTop);
_activeSubSpace->cacheRanges(_survivorMemorySubSpace, &_survivorSpaceBase, &_survivorSpaceTop);
/* assume that value of RS Overflow flag will not be changed until scavengeRememberedSet() call, so handle it first */
_isRememberedSetInOverflowAtTheBeginning = isRememberedSetInOverflowState();
_extensions->rememberedSet.startProcessingSublist();
}
void
MM_Scavenger::workerSetupForGC(MM_EnvironmentStandard *env)
{
OMRPORT_ACCESS_FROM_OMRPORT(env->getPortLibrary());
clearThreadGCStats(env, true);
/* This thread just started the scavenge task, record the timestamp.
* This must be done after clearThreadGCStats or else the timestamp will be cleared. */
env->_scavengerStats._workerScavengeStartTime = omrtime_hires_clock();
/* Clear local language-specific stats */
_delegate.workerSetupForGC_clearEnvironmentLangStats(env);
/* record that this thread is participating in this cycle */
env->_scavengerStats._gcCount = _extensions->scavengerStats._gcCount;
/* Reset the local remembered set fragment */
env->_scavengerRememberedSet.count = 0;
env->_scavengerRememberedSet.fragmentCurrent = NULL;
env->_scavengerRememberedSet.fragmentTop = NULL;
env->_scavengerRememberedSet.fragmentSize = (uintptr_t)OMR_SCV_REMSET_FRAGMENT_SIZE;
env->_scavengerRememberedSet.parentList = &_extensions->rememberedSet;
/* caches should all be reset */
Assert_MM_true(NULL == env->_survivorCopyScanCache);
Assert_MM_true(NULL == env->_tenureCopyScanCache);
Assert_MM_true(NULL == env->_deferredScanCache);
Assert_MM_true(NULL == env->_deferredCopyCache);
Assert_MM_false(env->_loaAllocation);
Assert_MM_true(NULL == env->_survivorTLHRemainderBase);
Assert_MM_true(NULL == env->_survivorTLHRemainderTop);
}
uintptr_t
MM_Scavenger::calculateMaxCacheCount(uintptr_t activeMemorySize)
{
return 5 * (activeMemorySize / (_extensions->scavengerScanCacheMaximumSize + _extensions->scavengerScanCacheMinimumSize));
}
void
MM_Scavenger::calculateRecommendedWorkingThreads(MM_EnvironmentStandard *env)
{
if (!_extensions->adaptiveThreadingEnabled() || _extensions->isConcurrentScavengerEnabled()) {
return;
}
Trc_MM_Scavenger_calculateRecommendedWorkingThreads_entry(env->getLanguageVMThread(), _extensions->scavengerStats._gcCount);
if (_isRememberedSetInOverflowAtTheBeginning || _extensions->scavengerStats._causedRememberedSetOverflow) {
/* Scavenge cycle ignored for recommending threads. Scavenger had overflows, this will skew the model,
* as this is the not the normal case for stalling ("Irregular" stalling with SyncAndReleaseMaster,
* this is not the norm hence we don't have to adjust for it) */
Trc_MM_Scavenger_calculateRecommendedWorkingThreads_exitOverflow(env->getLanguageVMThread());
return;
}
OMRPORT_ACCESS_FROM_OMRPORT(env->getPortLibrary());
uintptr_t totalThreads = _dispatcher->activeThreadCount();
/* Calculate the average time it takes the worker threads to start collection and avgerage time workers are idle waiting for task cleanup
* Calculated as (Sum_WorkerStartTime(t1 + t2 + ... + tn) - (n * collection_start)) / n */
uint64_t avgTimeToStartCollection = omrtime_hires_delta((_extensions->scavengerStats._startTime * totalThreads), _extensions->scavengerStats._workerScavengeStartTime, OMRPORT_TIME_DELTA_IN_MICROSECONDS) / totalThreads;
uint64_t avgTimeIdleAfterCollection = omrtime_hires_delta(_extensions->scavengerStats._workerScavengeEndTime, (_extensions->scavengerStats._endTime * totalThreads), OMRPORT_TIME_DELTA_IN_MICROSECONDS) / totalThreads;
/* Calculate average stall times */
uint64_t avgScanStallTime = omrtime_hires_delta(0, (_extensions->scavengerStats._workStallTime + _extensions->scavengerStats._completeStallTime), OMRPORT_TIME_DELTA_IN_MICROSECONDS) / totalThreads;
uint64_t avgSyncStallTime = omrtime_hires_delta(0, (_extensions->scavengerStats._adjustedSyncStallTime), OMRPORT_TIME_DELTA_IN_MICROSECONDS) / totalThreads;
uint64_t avgNotifyStallTime = omrtime_hires_delta(0, (_extensions->scavengerStats._notifyStallTime), OMRPORT_TIME_DELTA_IN_MICROSECONDS) / totalThreads;
Trc_MM_Scavenger_calculateRecommendedWorkingThreads_averageStallBreakDown(env->getLanguageVMThread(), totalThreads, avgTimeToStartCollection, avgTimeIdleAfterCollection, avgScanStallTime, avgSyncStallTime, avgNotifyStallTime);
uint64_t totalStallTime = avgTimeToStartCollection + avgTimeIdleAfterCollection + avgScanStallTime + avgSyncStallTime + avgNotifyStallTime;
uint64_t scavengeTotalTime = omrtime_hires_delta(_extensions->scavengerStats._startTime, _extensions->scavengerStats._endTime, OMRPORT_TIME_DELTA_IN_MICROSECONDS);
/* This Adaptive Threading Model aims to determine the efficiency of a cycle and predict the optimal GC thread count based on current number of threads,
* directly proportional to busy time and inversely proportional to idle times.
*
* The model can be expressed as a continues function, it's derived by finding a minimum of the folowing GC time function (used to project duration of GC for m threads,
* with oberved buys/stall times while performing GC with n threads):
*
* Time GC (m,n,b,s) = b * (n/m) + s * (m/n)^x
* Where m = number of threads for which total GC time (duration) is projected
* n = number of utilized threads (number of worker threads started + main thread) for the GC cycle used to observe s and b
* s = stall time per thread = average observed collection stall time for n threads = SUM(Stall time of n threads) / n
* b = busy time per thread = average collection busy time for n threads
* X = Stall Overhead Sensitivity/Tolerance, a model constant used to help model non-linear dependency of stall times on GC thread count
*
*
* Solving this function results in the model implementation expressed by expression 1 below. Expression 1 in combination with expression 2 gives up a complete implementation of the model
*
* (1) Number of Optimal Threads = m(n,b,s) = n * (B/X*s)^(1/X+1)
* (2) floor(((m(n,b,s) + H) * (1 - W)) + (n * W))
*
* Where W and H are constants, W = Weighted average factor, H = Thread Booster
*
* Expression (1) can be simplified to be written in terms of % stall and working threads as follows:
*
* b/s = (1/%stall) - 1
*
* ------------------------------------------------------------------
* | (1) m(n,b,s) = m(n,%stall) = n * ((1/x)*(1/%stall - 1)^(1/(x+1))|
* -------------------------------------------------------------------
*/
float percentStall = ((float) totalStallTime) / ((float) scavengeTotalTime);
float sensitivityFactor = _extensions->adaptiveThreadingSensitivityFactor;
float powerExponent = 1.0f / (sensitivityFactor + 1.0f);
float stallComponent = (1.0f / percentStall) - 1.0f;
float powerBase = (1.0f / sensitivityFactor) * stallComponent;
float idealThreads = totalThreads * powf(powerBase, powerExponent);
float adjustedAverage = MM_Math::weightedAverage((float)totalThreads, idealThreads, _extensions->adaptiveThreadingWeightActiveThreads);
_recommendedThreads = (uintptr_t)(adjustedAverage + _extensions->adaptiveThreadBooster);
if (_recommendedThreads < 2) {
_recommendedThreads = 2;
}
Trc_MM_Scavenger_calculateRecommendedWorkingThreads_setRecommendedThreads(env->getLanguageVMThread(), scavengeTotalTime, totalStallTime, (percentStall*100), totalThreads, idealThreads, adjustedAverage, (adjustedAverage + _extensions->adaptiveThreadBooster), _recommendedThreads);
}
/**
* Run a scavenge.
*/
void
MM_Scavenger::scavenge(MM_EnvironmentBase *envBase)
{
MM_EnvironmentStandard *env = MM_EnvironmentStandard::getEnvironment(envBase);
MM_ParallelScavengeTask scavengeTask(env, _dispatcher, this, env->_cycleState, _recommendedThreads);
_dispatcher->run(env, &scavengeTask);
/* remove all scan caches temporary allocated in Heap */
_scavengeCacheFreeList.removeAllHeapAllocatedChunks(env);
Assert_MM_true(_scavengeCacheFreeList.areAllCachesReturned());
Assert_MM_true(0 == _cachedEntryCount);
}
void
MM_Scavenger::reportScavengeStart(MM_EnvironmentStandard *env)
{
OMRPORT_ACCESS_FROM_OMRPORT(env->getPortLibrary());
TRIGGER_J9HOOK_MM_PRIVATE_SCAVENGE_START(
_extensions->privateHookInterface,
env->getOmrVMThread(),
omrtime_hires_clock(),
J9HOOK_MM_PRIVATE_SCAVENGE_START
);
}
void
MM_Scavenger::reportScavengeEnd(MM_EnvironmentStandard *env, bool lastIncrement)
{
OMRPORT_ACCESS_FROM_OMRPORT(env->getPortLibrary());
bool scavengeSuccessful = scavengeCompletedSuccessfully(env);
_delegate.reportScavengeEnd(env, scavengeSuccessful);
if (lastIncrement) {
_extensions->scavengerStats._tiltRatio = calculateTiltRatio();
Trc_MM_Tiltratio(env->getLanguageVMThread(), _extensions->scavengerStats._tiltRatio);
}
TRIGGER_J9HOOK_MM_PRIVATE_SCAVENGE_END(
_extensions->privateHookInterface,
env->getOmrVMThread(),
omrtime_hires_clock(),
J9HOOK_MM_PRIVATE_SCAVENGE_END,
env->_cycleState->_activeSubSpace,
lastIncrement
);
}
void
MM_Scavenger::reportGCStart(MM_EnvironmentStandard *env)
{
OMRPORT_ACCESS_FROM_OMRPORT(env->getPortLibrary());
/* TODO CRGTMP deprecate this trace point and add a new one */
Trc_MM_LocalGCStart(env->getLanguageVMThread(),
_extensions->globalGCStats.gcCount,
_extensions->scavengerStats._gcCount,
0, /* used to be weak reference count */
0, /* used to be soft reference count */
0, /* used to be phantom reference count */
0
);
Trc_OMRMM_LocalGCStart(env->getOmrVMThread(),
_extensions->globalGCStats.gcCount,
_extensions->scavengerStats._gcCount,
0, /* used to be weak reference count */
0, /* used to be soft reference count */
0, /* used to be phantom reference count */
0
);
TRIGGER_J9HOOK_MM_OMR_LOCAL_GC_START(
_extensions->omrHookInterface,
env->getOmrVMThread(),
omrtime_hires_clock(),
J9HOOK_MM_OMR_LOCAL_GC_START,
_extensions->globalGCStats.gcCount,
_extensions->scavengerStats._gcCount
);
}
void
MM_Scavenger::reportGCEnd(MM_EnvironmentStandard *env)
{
OMRPORT_ACCESS_FROM_ENVIRONMENT(env);
Trc_MM_LocalGCEnd(env->getLanguageVMThread(),
_extensions->incrementScavengerStats._rememberedSetOverflow,
_extensions->incrementScavengerStats._causedRememberedSetOverflow,
_extensions->incrementScavengerStats._scanCacheOverflow,
_extensions->incrementScavengerStats._failedFlipCount,
_extensions->incrementScavengerStats._failedFlipBytes,
_extensions->incrementScavengerStats._failedTenureCount,
_extensions->incrementScavengerStats._failedTenureBytes,
_extensions->incrementScavengerStats._flipCount,
_extensions->incrementScavengerStats._flipBytes,
_extensions->heap->getApproximateActiveFreeMemorySize(MEMORY_TYPE_NEW),
_extensions->heap->getActiveMemorySize(MEMORY_TYPE_NEW),
_extensions->heap->getApproximateActiveFreeMemorySize(MEMORY_TYPE_OLD),
_extensions->heap->getActiveMemorySize(MEMORY_TYPE_OLD),
(_extensions-> largeObjectArea ? _extensions->heap->getApproximateActiveFreeLOAMemorySize(MEMORY_TYPE_OLD) : (uintptr_t)0 ),
(_extensions-> largeObjectArea ? _extensions->heap->getActiveLOAMemorySize(MEMORY_TYPE_OLD) : (uintptr_t)0 ),
_extensions->incrementScavengerStats._tenureAge
);
Trc_OMRMM_LocalGCEnd(env->getOmrVMThread(),
_extensions->incrementScavengerStats._rememberedSetOverflow,
_extensions->incrementScavengerStats._causedRememberedSetOverflow,
_extensions->incrementScavengerStats._scanCacheOverflow,
_extensions->incrementScavengerStats._failedFlipCount,
_extensions->incrementScavengerStats._failedFlipBytes,
_extensions->incrementScavengerStats._failedTenureCount,
_extensions->incrementScavengerStats._failedTenureBytes,
_extensions->incrementScavengerStats._flipCount,
_extensions->incrementScavengerStats._flipBytes,
_extensions->heap->getApproximateActiveFreeMemorySize(MEMORY_TYPE_NEW),
_extensions->heap->getActiveMemorySize(MEMORY_TYPE_NEW),
_extensions->heap->getApproximateActiveFreeMemorySize(MEMORY_TYPE_OLD),
_extensions->heap->getActiveMemorySize(MEMORY_TYPE_OLD),
(_extensions-> largeObjectArea ? _extensions->heap->getApproximateActiveFreeLOAMemorySize(MEMORY_TYPE_OLD) : (uintptr_t)0 ),
(_extensions-> largeObjectArea ? _extensions->heap->getActiveLOAMemorySize(MEMORY_TYPE_OLD) : (uintptr_t)0 ),
_extensions->scavengerStats._tenureAge
);
TRIGGER_J9HOOK_MM_OMR_LOCAL_GC_END(
_extensions->omrHookInterface,
env->getOmrVMThread(),
omrtime_hires_clock(),
J9HOOK_MM_OMR_LOCAL_GC_END,
env->_cycleState->_activeSubSpace,
_extensions->globalGCStats.gcCount,
_extensions->incrementScavengerStats._gcCount,
_extensions->incrementScavengerStats._rememberedSetOverflow,
_extensions->incrementScavengerStats._causedRememberedSetOverflow,
_extensions->incrementScavengerStats._scanCacheOverflow,
_extensions->incrementScavengerStats._failedFlipCount,
_extensions->incrementScavengerStats._failedFlipBytes,
_extensions->incrementScavengerStats._failedTenureCount,
_extensions->incrementScavengerStats._failedTenureBytes,
_extensions->incrementScavengerStats._backout,
_extensions->incrementScavengerStats._flipCount,
_extensions->incrementScavengerStats._flipBytes,
_extensions->incrementScavengerStats._tenureAggregateCount,
_extensions->incrementScavengerStats._tenureAggregateBytes,
_extensions->tiltedScavenge ? 1 : 0,
_extensions->heap->getApproximateActiveFreeMemorySize(MEMORY_TYPE_NEW),
_extensions->heap->getActiveMemorySize(MEMORY_TYPE_NEW),
_extensions->heap->getApproximateActiveFreeMemorySize(MEMORY_TYPE_OLD),
_extensions->heap->getActiveMemorySize(MEMORY_TYPE_OLD),
(_extensions->largeObjectArea ? 1 : 0),
(_extensions->largeObjectArea ? _extensions->heap->getApproximateActiveFreeLOAMemorySize(MEMORY_TYPE_OLD) : 0),
(_extensions->largeObjectArea ? _extensions->heap->getActiveLOAMemorySize(MEMORY_TYPE_OLD) :0),
_extensions->incrementScavengerStats._tenureAge,
_extensions->heap->getMemorySize()
);
}
void
MM_Scavenger::clearThreadGCStats(MM_EnvironmentBase *env, bool firstIncrement)
{
env->_scavengerStats.clear(firstIncrement);
}
void
MM_Scavenger::clearIncrementGCStats(MM_EnvironmentBase *env, bool firstIncrement)
{
_extensions->incrementScavengerStats.clear(firstIncrement);
}
void
MM_Scavenger::clearCycleGCStats(MM_EnvironmentBase *env)
{
_extensions->scavengerStats.clear(true);
}
void
MM_Scavenger::mergeGCStatsBase(MM_EnvironmentBase *env, MM_ScavengerStats *finalGCStats, MM_ScavengerStats *scavStats)
{
finalGCStats->_rememberedSetOverflow |= scavStats->_rememberedSetOverflow;
finalGCStats->_causedRememberedSetOverflow |= scavStats->_causedRememberedSetOverflow;
finalGCStats->_scanCacheOverflow |= scavStats->_scanCacheOverflow;
finalGCStats->_scanCacheAllocationFromHeap |= scavStats->_scanCacheAllocationFromHeap;
finalGCStats->_scanCacheAllocationDurationDuringSavenger = OMR_MAX(finalGCStats->_scanCacheAllocationDurationDuringSavenger, scavStats->_scanCacheAllocationDurationDuringSavenger);
finalGCStats->_backout |= scavStats->_backout;
finalGCStats->_tenureAggregateCount += scavStats->_tenureAggregateCount;
finalGCStats->_tenureAggregateBytes += scavStats->_tenureAggregateBytes;
#if defined(OMR_GC_LARGE_OBJECT_AREA)
finalGCStats->_tenureLOACount += scavStats->_tenureLOACount;
finalGCStats->_tenureLOABytes += scavStats->_tenureLOABytes;
#endif /* OMR_GC_LARGE_OBJECT_AREA */
finalGCStats->_flipCount += scavStats->_flipCount;
finalGCStats->_flipBytes += scavStats->_flipBytes;
finalGCStats->_failedTenureCount += scavStats->_failedTenureCount;
finalGCStats->_failedTenureBytes += scavStats->_failedTenureBytes;
finalGCStats->_failedTenureLargest = OMR_MAX(scavStats->_failedTenureLargest,
finalGCStats->_failedTenureLargest);
finalGCStats->_failedFlipCount += scavStats->_failedFlipCount;
finalGCStats->_failedFlipBytes += scavStats->_failedFlipBytes;
#if defined(J9MODRON_TGC_PARALLEL_STATISTICS)
finalGCStats->_acquireFreeListCount += scavStats->_acquireFreeListCount;
finalGCStats->_releaseFreeListCount += scavStats->_releaseFreeListCount;
finalGCStats->_acquireScanListCount += scavStats->_acquireScanListCount;
finalGCStats->_releaseScanListCount += scavStats->_releaseScanListCount;
finalGCStats->_acquireListLockCount += scavStats->_acquireListLockCount;
finalGCStats->_aliasToCopyCacheCount += scavStats->_aliasToCopyCacheCount;
finalGCStats->_arraySplitCount += scavStats->_arraySplitCount;
finalGCStats->_arraySplitAmount += scavStats->_arraySplitAmount;
finalGCStats->_totalDeepStructures += scavStats->_totalDeepStructures;
finalGCStats->_totalObjsDeepScanned += scavStats->_totalObjsDeepScanned;
finalGCStats->_depthDeepestStructure = scavStats->_depthDeepestStructure;
finalGCStats->_copyScanUpdates += scavStats->_copyScanUpdates;
#endif /* J9MODRON_TGC_PARALLEL_STATISTICS */
finalGCStats->_flipDiscardBytes += scavStats->_flipDiscardBytes;
finalGCStats->_tenureDiscardBytes += scavStats->_tenureDiscardBytes;
finalGCStats->_survivorTLHRemainderCount += scavStats->_survivorTLHRemainderCount;
finalGCStats->_tenureTLHRemainderCount += scavStats->_tenureTLHRemainderCount;
finalGCStats->_semiSpaceAllocationCountLarge += scavStats->_semiSpaceAllocationCountLarge;
finalGCStats->_semiSpaceAllocationCountSmall += scavStats->_semiSpaceAllocationCountSmall;
finalGCStats->_tenureSpaceAllocationCountLarge += scavStats->_tenureSpaceAllocationCountLarge;
finalGCStats->_tenureSpaceAllocationCountSmall += scavStats->_tenureSpaceAllocationCountSmall;
/* TODO: Fix this. Not true when merging Main GC threads stats for standard (non CS) Scavenger.
Assert_MM_true(finalGCStats->_flipHistoryNewIndex == scavStats->_flipHistoryNewIndex); */
for (int i = 1; i <= OBJECT_HEADER_AGE_MAX+1; ++i) {
finalGCStats->getFlipHistory(0)->_flipBytes[i] += scavStats->getFlipHistory(0)->_flipBytes[i];
finalGCStats->getFlipHistory(0)->_tenureBytes[i] += scavStats->getFlipHistory(0)->_tenureBytes[i];
}
finalGCStats->_tenureExpandedBytes += scavStats->_tenureExpandedBytes;
finalGCStats->_tenureExpandedCount += scavStats->_tenureExpandedCount;
finalGCStats->_tenureExpandedTime += scavStats->_tenureExpandedTime;
#if defined(OMR_SCAVENGER_TRACK_COPY_DISTANCE)
for (uintptr_t i = 0; i < OMR_SCAVENGER_DISTANCE_BINS; i++) {
finalGCStats->_copy_distance_counts[i] += scavStats->_copy_distance_counts[i];
}
#endif /* OMR_SCAVENGER_TRACK_COPY_DISTANCE */
for (uintptr_t i = 0; i < OMR_SCAVENGER_CACHESIZE_BINS; i++) {
finalGCStats->_copy_cachesize_counts[i] += scavStats->_copy_cachesize_counts[i];
}
finalGCStats->_leafObjectCount += scavStats->_leafObjectCount;
finalGCStats->_copy_cachesize_sum += scavStats->_copy_cachesize_sum;
finalGCStats->_workStallTime += scavStats->_workStallTime;
finalGCStats->_completeStallTime += scavStats->_completeStallTime;
finalGCStats->_syncStallTime += scavStats->_syncStallTime;
finalGCStats->_workStallCount += scavStats->_workStallCount;
finalGCStats->_completeStallCount += scavStats->_completeStallCount;
_extensions->scavengerStats._syncStallCount += scavStats->_syncStallCount;
/* Adaptive Threading Stats */
finalGCStats->_workerScavengeStartTime += scavStats->_workerScavengeStartTime;
finalGCStats->_workerScavengeEndTime += scavStats->_workerScavengeEndTime;
finalGCStats->_notifyStallTime += scavStats->_notifyStallTime;
finalGCStats->_adjustedSyncStallTime += scavStats->_adjustedSyncStallTime;
}
void
MM_Scavenger::mergeThreadGCStats(MM_EnvironmentBase *env)
{
OMRPORT_ACCESS_FROM_OMRVM(_omrVM);
/* Protect the merge with the mutex (this is done by multiple threads in the parallel collector) */
omrthread_monitor_enter(_extensions->gcStatsMutex);
MM_ScavengerStats *scavStats = &env->_scavengerStats;
/* This thread is just about to complete the scavenge task, record the timestamp.
* This must be done before mergeGCStatsBase or else the timestamp won't be mereged as needed by adaptive threading. */
env->_scavengerStats._workerScavengeEndTime = omrtime_hires_clock();
mergeGCStatsBase(env, &_extensions->incrementScavengerStats, scavStats);
/* Merge language specific statistics. No known interesting data per increment - they are merged directly to aggregate cycle stats */
_delegate.mergeGCStats_mergeLangStats(env);
uint64_t timeToStartCollection = omrtime_hires_delta(_extensions->scavengerStats._startTime, scavStats->_workerScavengeStartTime, OMRPORT_TIME_DELTA_IN_MICROSECONDS);
uint64_t scanStall = omrtime_hires_delta(0, (scavStats->_workStallTime + scavStats->_completeStallTime), OMRPORT_TIME_DELTA_IN_MICROSECONDS);
uint64_t syncStall = omrtime_hires_delta(0, (scavStats->_adjustedSyncStallTime), OMRPORT_TIME_DELTA_IN_MICROSECONDS);
uint64_t notifyStallTime = omrtime_hires_delta(0, (scavStats->_notifyStallTime), OMRPORT_TIME_DELTA_IN_MICROSECONDS);
Trc_MM_Scavenger_calculateRecommendedWorkingThreads_threadStallBreakDown(env->getLanguageVMThread(), env->getWorkerID(), timeToStartCollection, scanStall, syncStall, notifyStallTime);
omrthread_monitor_exit(_extensions->gcStatsMutex);
/* record the thread-specific parallelism stats in the trace buffer. This aprtially duplicates info in -Xtgc:parallel */
Trc_MM_ParallelScavenger_parallelStats(
env->getLanguageVMThread(),
(uint32_t)env->getWorkerID(),
(uint32_t)omrtime_hires_delta(0, scavStats->_workStallTime, OMRPORT_TIME_DELTA_IN_MILLISECONDS),
(uint32_t)omrtime_hires_delta(0, scavStats->_completeStallTime, OMRPORT_TIME_DELTA_IN_MILLISECONDS),
(uint32_t)omrtime_hires_delta(0, scavStats->_syncStallTime, OMRPORT_TIME_DELTA_IN_MILLISECONDS),
(uint32_t)scavStats->_workStallCount,
(uint32_t)scavStats->_completeStallCount,
(uint32_t)scavStats->_syncStallCount,
scavStats->_acquireFreeListCount,
scavStats->_releaseFreeListCount,
scavStats->_acquireScanListCount,
scavStats->_releaseScanListCount);
}
void
MM_Scavenger::mergeIncrementGCStats(MM_EnvironmentBase *env, bool lastIncrement)
{
Assert_MM_true(env->isMainThread());
MM_ScavengerStats *finalGCStats = &_extensions->scavengerStats;
mergeGCStatsBase(env, finalGCStats, &_extensions->incrementScavengerStats);
/* Language specific stats were supposed to be merged directly from thread local to cycle global. No need to merge them here. */
if (lastIncrement) {
/* Calculate new tenure age */
finalGCStats->getFlipHistory(0)->_tenureMask = _tenureMask;
uintptr_t tenureAge = 0;
for (tenureAge = 0; tenureAge <= OBJECT_HEADER_AGE_MAX; ++tenureAge) {
if (_tenureMask & ((uintptr_t)1 << tenureAge)) {
break;
}
}
finalGCStats->_tenureAge = tenureAge;
/* Update historical flip stats for age 0 */
MM_ScavengerStats::FlipHistory* flipHistoryPrevious = finalGCStats->getFlipHistory(1);
flipHistoryPrevious->_flipBytes[0] = finalGCStats->_semiSpaceAllocBytesAcumulation;
flipHistoryPrevious->_tenureBytes[0] = finalGCStats->_tenureSpaceAllocBytesAcumulation;
finalGCStats->_semiSpaceAllocBytesAcumulation = 0;
finalGCStats->_tenureSpaceAllocBytesAcumulation = 0;
}
}
/**
* Determine whether GC stats should be calculated for this round.
* @return true if GC stats should be calculated for this round, false otherwise.
*/
bool
MM_Scavenger::canCalcGCStats(MM_EnvironmentStandard *env)
{
#if defined(OMR_GC_CONCURRENT_SCAVENGER)
/* Only do once, at the end of cycle */
bool canCalculate = !isConcurrentCycleInProgress();
#else
bool canCalculate = true;
#endif
/* If no backout and we actually did a scavenge this time around then it's safe to gather stats */
canCalculate &= (!isBackOutFlagRaised() && (0 < _extensions->heap->getPercolateStats()->getScavengesSincePercolate()));
return canCalculate;
}
/**
* Calculate any GC stats after a collection.
*/
void
MM_Scavenger::calcGCStats(MM_EnvironmentStandard *env)
{
/* Do not calculate stats unless we actually collected */
if (canCalcGCStats(env)) {
MM_ScavengerStats *scavengerGCStats;
scavengerGCStats = &_extensions->scavengerStats;
uintptr_t initialFree = env->_cycleState->_activeSubSpace->getActualActiveFreeMemorySize();
uintptr_t tenureAggregateBytes = 0;
float tenureBytesDeviation = 0;
/* First collection ? */
if (scavengerGCStats->_gcCount > 1 ) {
scavengerGCStats->_avgInitialFree = (uintptr_t)MM_Math::weightedAverage((float)scavengerGCStats->_avgInitialFree, (float)initialFree, INITIAL_FREE_HISTORY_WEIGHT);
#if defined(OMR_GC_LARGE_OBJECT_AREA)
tenureAggregateBytes = scavengerGCStats->_tenureAggregateBytes - scavengerGCStats->_tenureLOABytes;
scavengerGCStats->_avgTenureLOABytes = (uintptr_t)MM_Math::weightedAverage((float)scavengerGCStats->_avgTenureLOABytes,
(float)scavengerGCStats->_tenureLOABytes,
TENURE_BYTES_HISTORY_WEIGHT);
#else /* OMR_GC_LARGE_OBJECT_AREA */
tenureAggregateBytes = scavengerGCStats->_tenureAggregateBytes;
#endif /* OMR_GC_LARGE_OBJECT_AREA */
scavengerGCStats->_avgTenureBytes = (uintptr_t)MM_Math::weightedAverage((float)scavengerGCStats->_avgTenureBytes,
(float)tenureAggregateBytes,
TENURE_BYTES_HISTORY_WEIGHT);
tenureBytesDeviation = (float)tenureAggregateBytes - scavengerGCStats->_avgTenureBytes;
scavengerGCStats->_avgTenureBytesDeviation = (uintptr_t)MM_Math::weightedAverage((float)scavengerGCStats->_avgTenureBytesDeviation,
MM_Math::abs(tenureBytesDeviation),
TENURE_BYTES_HISTORY_WEIGHT);
} else {
scavengerGCStats->_avgInitialFree = initialFree;
/* We can assume that in the first GC, about half of the objects are long lived objects, so we use this heuristic to give a rough estimate for the starting point */
scavengerGCStats->_avgTenureBytes = (uintptr_t)(scavengerGCStats->_flipBytes / 2);
}
#if defined(OMR_GC_MODRON_CONCURRENT_MARK)
if (_extensions->debugConcurrentMark) {
OMRPORT_ACCESS_FROM_OMRPORT(env->getPortLibrary());
omrtty_printf("Tenured bytes: %zu\navgTenureBytes: %zu\ntenureBytesDeviation: %f\navgTenureBytesDeviation: %zu\n",
tenureAggregateBytes,
scavengerGCStats->_avgTenureBytes,
tenureBytesDeviation,
scavengerGCStats->_avgTenureBytesDeviation);
}
#endif /* OMR_GC_MODRON_CONCURRENT_MARK */
}
}
/****************************************
* Copy/forward routines
****************************************
*/
uintptr_t
MM_Scavenger::calculateCopyScanCacheSizeForWaitingThreads(uintptr_t maxCacheSize, uintptr_t threadCount, uintptr_t waitingThreads)
{
uintptr_t minCacheSize = _extensions->scavengerScanCacheMinimumSize;
uintptr_t range = maxCacheSize - minCacheSize;
uintptr_t minTLHSize = _extensions->tlhMinimumSize;
uintptr_t step = range / minTLHSize;
uintptr_t multiplier = (step * (threadCount - waitingThreads)) / threadCount;
uintptr_t cacheSize = (minTLHSize * multiplier) + minCacheSize;