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#include "precompiled.hpp"
#include "gc/shenandoah/heuristics/shenandoahAdaptiveHeuristics.hpp"
#include "gc/shenandoah/shenandoahCollectionSet.hpp"
#include "gc/shenandoah/shenandoahFreeSet.hpp"
! #include "gc/shenandoah/shenandoahHeap.inline.hpp"
#include "gc/shenandoah/shenandoahHeapRegion.inline.hpp"
#include "logging/log.hpp"
#include "logging/logTag.hpp"
#include "utilities/quickSort.hpp"
// These constants are used to adjust the margin of error for the moving
#include "precompiled.hpp"
#include "gc/shenandoah/heuristics/shenandoahAdaptiveHeuristics.hpp"
#include "gc/shenandoah/shenandoahCollectionSet.hpp"
#include "gc/shenandoah/shenandoahFreeSet.hpp"
! #include "gc/shenandoah/shenandoahGeneration.hpp"
#include "gc/shenandoah/shenandoahHeapRegion.inline.hpp"
+ #include "gc/shenandoah/shenandoahYoungGeneration.hpp"
#include "logging/log.hpp"
#include "logging/logTag.hpp"
#include "utilities/quickSort.hpp"
// These constants are used to adjust the margin of error for the moving
// that the true value of our estimate is outside the interval. These are used
// as bounds on the adjustments applied at the outcome of a GC cycle.
const double ShenandoahAdaptiveHeuristics::MINIMUM_CONFIDENCE = 0.319; // 25%
const double ShenandoahAdaptiveHeuristics::MAXIMUM_CONFIDENCE = 3.291; // 99.9%
! ShenandoahAdaptiveHeuristics::ShenandoahAdaptiveHeuristics() :
! ShenandoahHeuristics(),
_margin_of_error_sd(ShenandoahAdaptiveInitialConfidence),
_spike_threshold_sd(ShenandoahAdaptiveInitialSpikeThreshold),
_last_trigger(OTHER) { }
ShenandoahAdaptiveHeuristics::~ShenandoahAdaptiveHeuristics() {}
void ShenandoahAdaptiveHeuristics::choose_collection_set_from_regiondata(ShenandoahCollectionSet* cset,
RegionData* data, size_t size,
size_t actual_free) {
size_t garbage_threshold = ShenandoahHeapRegion::region_size_bytes() * ShenandoahGarbageThreshold / 100;
// The logic for cset selection in adaptive is as follows:
//
// 1. We cannot get cset larger than available free space. Otherwise we guarantee OOME
// during evacuation, and thus guarantee full GC. In practice, we also want to let
// that the true value of our estimate is outside the interval. These are used
// as bounds on the adjustments applied at the outcome of a GC cycle.
const double ShenandoahAdaptiveHeuristics::MINIMUM_CONFIDENCE = 0.319; // 25%
const double ShenandoahAdaptiveHeuristics::MAXIMUM_CONFIDENCE = 3.291; // 99.9%
! ShenandoahAdaptiveHeuristics::ShenandoahAdaptiveHeuristics(ShenandoahGeneration* generation) :
! ShenandoahHeuristics(generation),
_margin_of_error_sd(ShenandoahAdaptiveInitialConfidence),
_spike_threshold_sd(ShenandoahAdaptiveInitialSpikeThreshold),
_last_trigger(OTHER) { }
ShenandoahAdaptiveHeuristics::~ShenandoahAdaptiveHeuristics() {}
void ShenandoahAdaptiveHeuristics::choose_collection_set_from_regiondata(ShenandoahCollectionSet* cset,
RegionData* data, size_t size,
size_t actual_free) {
size_t garbage_threshold = ShenandoahHeapRegion::region_size_bytes() * ShenandoahGarbageThreshold / 100;
+ size_t ignore_threshold = ShenandoahHeapRegion::region_size_bytes() * ShenandoahIgnoreGarbageThreshold / 100;
+ ShenandoahHeap* heap = ShenandoahHeap::heap();
// The logic for cset selection in adaptive is as follows:
//
// 1. We cannot get cset larger than available free space. Otherwise we guarantee OOME
// during evacuation, and thus guarantee full GC. In practice, we also want to let
// Therefore, we start by sorting the regions by garbage. Then we unconditionally add the best candidates
// before we meet min_garbage. Then we add all candidates that fit with a garbage threshold before
// we hit max_cset. When max_cset is hit, we terminate the cset selection. Note that in this scheme,
// ShenandoahGarbageThreshold is the soft threshold which would be ignored until min_garbage is hit.
! size_t capacity = ShenandoahHeap::heap()->soft_max_capacity();
! size_t max_cset = (size_t)((1.0 * capacity / 100 * ShenandoahEvacReserve) / ShenandoahEvacWaste);
! size_t free_target = (capacity / 100 * ShenandoahMinFreeThreshold) + max_cset;
! size_t min_garbage = (free_target > actual_free ? (free_target - actual_free) : 0);
! log_info(gc, ergo)("Adaptive CSet Selection. Target Free: " SIZE_FORMAT "%s, Actual Free: "
! SIZE_FORMAT "%s, Max CSet: " SIZE_FORMAT "%s, Min Garbage: " SIZE_FORMAT "%s",
! byte_size_in_proper_unit(free_target), proper_unit_for_byte_size(free_target),
! byte_size_in_proper_unit(actual_free), proper_unit_for_byte_size(actual_free),
- byte_size_in_proper_unit(max_cset), proper_unit_for_byte_size(max_cset),
- byte_size_in_proper_unit(min_garbage), proper_unit_for_byte_size(min_garbage));
// Better select garbage-first regions
QuickSort::sort<RegionData>(data, (int)size, compare_by_garbage, false);
! size_t cur_cset = 0;
! size_t cur_garbage = 0;
!
! for (size_t idx = 0; idx < size; idx++) {
! ShenandoahHeapRegion* r = data[idx]._region;
!
! size_t new_cset = cur_cset + r->get_live_data_bytes();
! size_t new_garbage = cur_garbage + r->garbage();
!
! if (new_cset > max_cset) {
! break;
}
!
! if ((new_garbage < min_garbage) || (r->garbage() > garbage_threshold)) {
! cset->add_region(r);
! cur_cset = new_cset;
! cur_garbage = new_garbage;
}
}
}
void ShenandoahAdaptiveHeuristics::record_cycle_start() {
ShenandoahHeuristics::record_cycle_start();
_allocation_rate.allocation_counter_reset();
}
! void ShenandoahAdaptiveHeuristics::record_success_concurrent() {
! ShenandoahHeuristics::record_success_concurrent();
size_t available = ShenandoahHeap::heap()->free_set()->available();
_available.add(available);
double z_score = 0.0;
// Therefore, we start by sorting the regions by garbage. Then we unconditionally add the best candidates
// before we meet min_garbage. Then we add all candidates that fit with a garbage threshold before
// we hit max_cset. When max_cset is hit, we terminate the cset selection. Note that in this scheme,
// ShenandoahGarbageThreshold is the soft threshold which would be ignored until min_garbage is hit.
! // In generational mode, the sort order within the data array is not strictly descending amounts of garbage. In
! // particular, regions that have reached tenure age will be sorted into this array before younger regions that contain
! // more garbage. This represents one of the reasons why we keep looking at regions even after we decide, for example,
! // to exclude one of the regions because it might require evacuation of too much live data.
+ bool is_generational = heap->mode()->is_generational();
+ bool is_global = (_generation->generation_mode() == GLOBAL);
+ size_t capacity = heap->young_generation()->max_capacity();
! // cur_young_garbage represents the amount of memory to be reclaimed from young-gen. In the case that live objects
! // are known to be promoted out of young-gen, we count this as cur_young_garbage because this memory is reclaimed
! // from young-gen and becomes available to serve future young-gen allocation requests.
! size_t cur_young_garbage = 0;
// Better select garbage-first regions
QuickSort::sort<RegionData>(data, (int)size, compare_by_garbage, false);
! if (is_generational) {
! if (is_global) {
! size_t max_young_cset = (size_t) (heap->get_young_evac_reserve() / ShenandoahEvacWaste);
! size_t young_cur_cset = 0;
! size_t max_old_cset = (size_t) (heap->get_old_evac_reserve() / ShenandoahEvacWaste);
! size_t old_cur_cset = 0;
! size_t free_target = (capacity * ShenandoahMinFreeThreshold) / 100 + max_young_cset;
! size_t min_garbage = (free_target > actual_free) ? (free_target - actual_free) : 0;
!
! log_info(gc, ergo)("Adaptive CSet Selection for GLOBAL. Max Young Cset: " SIZE_FORMAT
! "%s, Max Old CSet: " SIZE_FORMAT "%s, Actual Free: " SIZE_FORMAT "%s.",
+ byte_size_in_proper_unit(max_young_cset), proper_unit_for_byte_size(max_young_cset),
+ byte_size_in_proper_unit(max_old_cset), proper_unit_for_byte_size(max_old_cset),
+ byte_size_in_proper_unit(actual_free), proper_unit_for_byte_size(actual_free));
+
+ for (size_t idx = 0; idx < size; idx++) {
+ ShenandoahHeapRegion* r = data[idx]._region;
+ bool add_region = false;
+ if (r->is_old()) {
+ size_t new_cset = old_cur_cset + r->get_live_data_bytes();
+ if ((new_cset <= max_old_cset) && (r->garbage() > garbage_threshold)) {
+ add_region = true;
+ old_cur_cset = new_cset;
+ }
+ } else if (cset->is_preselected(r->index())) {
+ assert(r->age() >= InitialTenuringThreshold, "Preselected regions must have tenure age");
+ // Entire region will be promoted, This region does not impact young-gen or old-gen evacuation reserve.
+ // This region has been pre-selected and its impact on promotion reserve is already accounted for.
+ add_region = true;
+ // r->used() is r->garbage() + r->get_live_data_bytes()
+ // Since all live data in this region is being evacuated from young-gen, it is as if this memory
+ // is garbage insofar as young-gen is concerned. Counting this as garbage reduces the need to
+ // reclaim highly utilized young-gen regions just for the sake of finding min_garbage to reclaim
+ // within youn-gen memory.
+ cur_young_garbage += r->used();
+ } else if (r->age() < InitialTenuringThreshold) {
+ size_t new_cset = young_cur_cset + r->get_live_data_bytes();
+ size_t region_garbage = r->garbage();
+ size_t new_garbage = cur_young_garbage + region_garbage;
+ bool add_regardless = (region_garbage > ignore_threshold) && (new_garbage < min_garbage);
+ if ((new_cset <= max_young_cset) && (add_regardless || (region_garbage > garbage_threshold))) {
+ add_region = true;
+ young_cur_cset = new_cset;
+ cur_young_garbage = new_garbage;
+ }
+ }
+ // Note that we do not add aged regions if they were not pre-selected. The reason they were not preselected
+ // is because there is not sufficient room in old-gen to hold their to-be-promoted live objects.
+
+ if (add_region) {
+ cset->add_region(r);
+ }
+ }
+ } else {
+ // This is young-gen collection or a mixed evacuation. If this is mixed evacuation, the old-gen candidate regions
+ // have already been added.
+ size_t max_cset = (size_t) (heap->get_young_evac_reserve() / ShenandoahEvacWaste);
+ size_t cur_cset = 0;
+ size_t free_target = (capacity * ShenandoahMinFreeThreshold) / 100 + max_cset;
+ size_t min_garbage = (free_target > actual_free) ? (free_target - actual_free) : 0;
+
+ log_info(gc, ergo)("Adaptive CSet Selection for YOUNG. Max CSet: " SIZE_FORMAT "%s, Actual Free: " SIZE_FORMAT "%s.",
+ byte_size_in_proper_unit(max_cset), proper_unit_for_byte_size(max_cset),
+ byte_size_in_proper_unit(actual_free), proper_unit_for_byte_size(actual_free));
+
+ for (size_t idx = 0; idx < size; idx++) {
+ ShenandoahHeapRegion* r = data[idx]._region;
+ size_t new_cset;
+ size_t region_garbage = r->garbage();
+ size_t new_garbage = cur_young_garbage + region_garbage;
+ bool add_region = false;
+
+ if (!r->is_old()) {
+ if (cset->is_preselected(r->index())) {
+ assert(r->age() >= InitialTenuringThreshold, "Preselected regions must have tenure age");
+ // Entire region will be promoted, This region does not impact young-gen evacuation reserve. Memory has already
+ // been set aside to hold evacuation results as advance_promotion_reserve.
+ add_region = true;
+ new_cset = cur_cset;
+ // Since all live data in this region is being evacuated from young-gen, it is as if this memory
+ // is garbage insofar as young-gen is concerned. Counting this as garbage reduces the need to
+ // reclaim highly utilized young-gen regions just for the sake of finding min_garbage to reclaim
+ // within youn-gen memory
+ cur_young_garbage += r->get_live_data_bytes();
+ } else if (r->age() < InitialTenuringThreshold) {
+ new_cset = cur_cset + r->get_live_data_bytes();
+ size_t region_garbage = r->garbage();
+ size_t new_garbage = cur_young_garbage + region_garbage;
+ bool add_regardless = (region_garbage > ignore_threshold) && (new_garbage < min_garbage);
+ if ((new_cset <= max_cset) && (add_regardless || (region_garbage > garbage_threshold))) {
+ add_region = true;
+ cur_cset = new_cset;
+ cur_young_garbage = new_garbage;
+ }
+ }
+ // Note that we do not add aged regions if they were not pre-selected. The reason they were not preselected
+ // is because there is not sufficient room in old-gen to hold their to-be-promoted live objects.
+
+ if (add_region) {
+ cset->add_region(r);
+ }
+ }
+ }
}
! } else {
! // Traditional Shenandoah (non-generational)
! size_t max_cset = (size_t) (heap->get_young_evac_reserve() / ShenandoahEvacWaste);
! size_t cur_cset = 0;
! size_t free_target = (capacity * ShenandoahMinFreeThreshold) / 100 + max_cset;
+ size_t min_garbage = (free_target > actual_free) ? (free_target - actual_free) : 0;
+
+ log_info(gc, ergo)("Adaptive CSet Selection. Max CSet: " SIZE_FORMAT "%s, Actual Free: " SIZE_FORMAT "%s.",
+ byte_size_in_proper_unit(max_cset), proper_unit_for_byte_size(max_cset),
+ byte_size_in_proper_unit(actual_free), proper_unit_for_byte_size(actual_free));
+
+ for (size_t idx = 0; idx < size; idx++) {
+ ShenandoahHeapRegion* r = data[idx]._region;
+ size_t new_cset = cur_cset + r->get_live_data_bytes();
+ size_t region_garbage = r->garbage();
+ size_t new_garbage = cur_young_garbage + region_garbage;
+ bool add_regardless = (region_garbage > ignore_threshold) && (new_garbage < min_garbage);
+ if ((new_cset <= max_cset) && (add_regardless || (region_garbage > garbage_threshold))) {
+ cset->add_region(r);
+ cur_cset = new_cset;
+ cur_young_garbage = new_garbage;
+ }
}
}
}
void ShenandoahAdaptiveHeuristics::record_cycle_start() {
ShenandoahHeuristics::record_cycle_start();
_allocation_rate.allocation_counter_reset();
}
! void ShenandoahAdaptiveHeuristics::record_success_concurrent(bool abbreviated) {
! ShenandoahHeuristics::record_success_concurrent(abbreviated);
size_t available = ShenandoahHeap::heap()->free_set()->available();
_available.add(available);
double z_score = 0.0;
static double saturate(double value, double min, double max) {
return MAX2(MIN2(value, max), min);
}
bool ShenandoahAdaptiveHeuristics::should_start_gc() {
! ShenandoahHeap* heap = ShenandoahHeap::heap();
! size_t max_capacity = heap->max_capacity();
! size_t capacity = heap->soft_max_capacity();
! size_t available = heap->free_set()->available();
! size_t allocated = heap->bytes_allocated_since_gc_start();
// Make sure the code below treats available without the soft tail.
size_t soft_tail = max_capacity - capacity;
available = (available > soft_tail) ? (available - soft_tail) : 0;
// Track allocation rate even if we decide to start a cycle for other reasons.
double rate = _allocation_rate.sample(allocated);
_last_trigger = OTHER;
! size_t min_threshold = capacity / 100 * ShenandoahMinFreeThreshold;
! if (available < min_threshold) {
! log_info(gc)("Trigger: Free (" SIZE_FORMAT "%s) is below minimum threshold (" SIZE_FORMAT "%s)",
byte_size_in_proper_unit(available), proper_unit_for_byte_size(available),
byte_size_in_proper_unit(min_threshold), proper_unit_for_byte_size(min_threshold));
return true;
}
const size_t max_learn = ShenandoahLearningSteps;
if (_gc_times_learned < max_learn) {
size_t init_threshold = capacity / 100 * ShenandoahInitFreeThreshold;
! if (available < init_threshold) {
! log_info(gc)("Trigger: Learning " SIZE_FORMAT " of " SIZE_FORMAT ". Free (" SIZE_FORMAT "%s) is below initial threshold (" SIZE_FORMAT "%s)",
! _gc_times_learned + 1, max_learn,
byte_size_in_proper_unit(available), proper_unit_for_byte_size(available),
byte_size_in_proper_unit(init_threshold), proper_unit_for_byte_size(init_threshold));
return true;
}
}
! // Check if allocation headroom is still okay. This also factors in:
! // 1. Some space to absorb allocation spikes
! // 2. Accumulated penalties from Degenerated and Full GC
! size_t allocation_headroom = available;
- size_t spike_headroom = capacity / 100 * ShenandoahAllocSpikeFactor;
- size_t penalties = capacity / 100 * _gc_time_penalties;
! allocation_headroom -= MIN2(allocation_headroom, spike_headroom);
! allocation_headroom -= MIN2(allocation_headroom, penalties);
double avg_cycle_time = _gc_time_history->davg() + (_margin_of_error_sd * _gc_time_history->dsd());
double avg_alloc_rate = _allocation_rate.upper_bound(_margin_of_error_sd);
if (avg_cycle_time > allocation_headroom / avg_alloc_rate) {
! log_info(gc)("Trigger: Average GC time (%.2f ms) is above the time for average allocation rate (%.0f %sB/s) to deplete free headroom (" SIZE_FORMAT "%s) (margin of error = %.2f)",
! avg_cycle_time * 1000,
byte_size_in_proper_unit(avg_alloc_rate), proper_unit_for_byte_size(avg_alloc_rate),
byte_size_in_proper_unit(allocation_headroom), proper_unit_for_byte_size(allocation_headroom),
_margin_of_error_sd);
log_info(gc, ergo)("Free headroom: " SIZE_FORMAT "%s (free) - " SIZE_FORMAT "%s (spike) - " SIZE_FORMAT "%s (penalties) = " SIZE_FORMAT "%s",
static double saturate(double value, double min, double max) {
return MAX2(MIN2(value, max), min);
}
bool ShenandoahAdaptiveHeuristics::should_start_gc() {
! size_t max_capacity = _generation->max_capacity();
! size_t capacity = _generation->soft_max_capacity();
! size_t available = _generation->available();
! size_t allocated = _generation->bytes_allocated_since_gc_start();
!
+ log_debug(gc)("should_start_gc (%s)? available: " SIZE_FORMAT ", soft_max_capacity: " SIZE_FORMAT
+ ", max_capacity: " SIZE_FORMAT ", allocated: " SIZE_FORMAT,
+ _generation->name(), available, capacity, max_capacity, allocated);
// Make sure the code below treats available without the soft tail.
size_t soft_tail = max_capacity - capacity;
available = (available > soft_tail) ? (available - soft_tail) : 0;
+ // The collector reserve may eat into what the mutator is allowed to use. Make sure we are looking
+ // at what is available to the mutator when deciding whether to start a GC.
+ size_t usable = ShenandoahHeap::heap()->free_set()->available();
+ if (usable < available) {
+ log_debug(gc)("Usable (" SIZE_FORMAT "%s) is less than available (" SIZE_FORMAT "%s)",
+ byte_size_in_proper_unit(usable), proper_unit_for_byte_size(usable),
+ byte_size_in_proper_unit(available), proper_unit_for_byte_size(available));
+ available = usable;
+ }
+
+ // Allocation spikes are a characteristic of both the application ahd the JVM configuration. On the JVM command line,
+ // the application developer may want to supply a hint of the nature of spikes that are inherent in the application
+ // workload, and this information would normally be independent of heap size (not a percentage thereof). On the
+ // other hand, some allocation spikes are correlated with JVM configuration. For example, there are allocation
+ // spikes at the starts of concurrent marking and evacuation to refresh all local allocation buffers. The nature
+ // of these spikes is determined by LAB min and max sizes and numbers of threads, but also on frequency of GC passes,
+ // and on "periodic" behavior of these threads If GC frequency is much higher than the periodic trigger for mutator
+ // threads, then many of the mutator threads may be able to "sit out" of most GC passes. Though the thread's stack
+ // must be scanned, the thread does not need to refresh its LABs if it sits idle throughout the duration of the GC
+ // pass. The best prediction for this aspect of spikes in allocation patterns is probably recent past history.
+ // TODO: and dive deeper into _gc_time_penalties as this may also need to be corrected
+
+ // Check if allocation headroom is still okay. This also factors in:
+ // 1. Some space to absorb allocation spikes (ShenandoahAllocSpikeFactor)
+ // 2. Accumulated penalties from Degenerated and Full GC
+ size_t allocation_headroom = available;
+ size_t spike_headroom = capacity / 100 * ShenandoahAllocSpikeFactor;
+ size_t penalties = capacity / 100 * _gc_time_penalties;
+
+ allocation_headroom -= MIN2(allocation_headroom, penalties);
+ allocation_headroom -= MIN2(allocation_headroom, spike_headroom);
+
// Track allocation rate even if we decide to start a cycle for other reasons.
double rate = _allocation_rate.sample(allocated);
_last_trigger = OTHER;
! size_t min_threshold = min_free_threshold();
!
! if (allocation_headroom < min_threshold) {
+ log_info(gc)("Trigger (%s): Free (" SIZE_FORMAT "%s) is below minimum threshold (" SIZE_FORMAT "%s)",
+ _generation->name(),
byte_size_in_proper_unit(available), proper_unit_for_byte_size(available),
byte_size_in_proper_unit(min_threshold), proper_unit_for_byte_size(min_threshold));
return true;
}
+ // Check if we need to learn a bit about the application
const size_t max_learn = ShenandoahLearningSteps;
if (_gc_times_learned < max_learn) {
size_t init_threshold = capacity / 100 * ShenandoahInitFreeThreshold;
! if (allocation_headroom < init_threshold) {
! log_info(gc)("Trigger (%s): Learning " SIZE_FORMAT " of " SIZE_FORMAT ". Free (" SIZE_FORMAT "%s) is below initial threshold (" SIZE_FORMAT "%s)",
! _generation->name(), _gc_times_learned + 1, max_learn,
byte_size_in_proper_unit(available), proper_unit_for_byte_size(available),
byte_size_in_proper_unit(init_threshold), proper_unit_for_byte_size(init_threshold));
return true;
}
}
! // Rationale:
! // The idea is that there is an average allocation rate and there are occasional abnormal bursts (or spikes) of
! // allocations that exceed the average allocation rate. What do these spikes look like?
! //
+ // 1. At certain phase changes, we may discard large amounts of data and replace it with large numbers of newly
+ // allocated objects. This "spike" looks more like a phase change. We were in steady state at M bytes/sec
+ // allocation rate and now we're in a "reinitialization phase" that looks like N bytes/sec. We need the "spike"
+ // accomodation to give us enough runway to recalibrate our "average allocation rate".
+ //
+ // 2. The typical workload changes. "Suddenly", our typical workload of N TPS increases to N+delta TPS. This means
+ // our average allocation rate needs to be adjusted. Once again, we need the "spike" accomodation to give us
+ // enough runway to recalibrate our "average allocation rate".
+ //
+ // 3. Though there is an "average" allocation rate, a given workload's demand for allocation may be very bursty. We
+ // allocate a bunch of LABs during the 5 ms that follow completion of a GC, then we perform no more allocations for
+ // the next 150 ms. It seems we want the "spike" to represent the maximum divergence from average within the
+ // period of time between consecutive evaluation of the should_start_gc() service. Here's the thinking:
+ //
+ // a) Between now and the next time I ask whether should_start_gc(), we might experience a spike representing
+ // the anticipated burst of allocations. If that would put us over budget, then we should start GC immediately.
+ // b) Between now and the anticipated depletion of allocation pool, there may be two or more bursts of allocations.
+ // If there are more than one of these bursts, we can "approximate" that these will be separated by spans of
+ // time with very little or no allocations so the "average" allocation rate should be a suitable approximation
+ // of how this will behave.
+ //
+ // For cases 1 and 2, we need to "quickly" recalibrate the average allocation rate whenever we detect a change
+ // in operation mode. We want some way to decide that the average rate has changed. Make average allocation rate
+ // computations an independent effort.
! // TODO: Account for inherent delays in responding to GC triggers
! // 1. It has been observed that delays of 200 ms or greater are common between the moment we return true from should_start_gc()
+ // and the moment at which we begin execution of the concurrent reset phase. Add this time into the calculation of
+ // avg_cycle_time below. (What is "this time"? Perhaps we should remember recent history of this delay for the
+ // running workload and use the maximum delay recently seen for "this time".)
+ // 2. The frequency of inquiries to should_start_gc() is adaptive, ranging between ShenandoahControlIntervalMin and
+ // ShenandoahControlIntervalMax. The current control interval (or the max control interval) should also be added into
+ // the calculation of avg_cycle_time below.
double avg_cycle_time = _gc_time_history->davg() + (_margin_of_error_sd * _gc_time_history->dsd());
+
+ size_t last_live_memory = get_last_live_memory();
+ size_t penultimate_live_memory = get_penultimate_live_memory();
+ double original_cycle_time = avg_cycle_time;
+ if ((penultimate_live_memory < last_live_memory) && (penultimate_live_memory != 0)) {
+ // If the live-memory size is growing, our estimates of cycle time are based on lighter workload, so adjust.
+ // TODO: Be more precise about how to scale when live memory is growing. Existing code is a very rough approximation
+ // tuned with very limited workload observations.
+ avg_cycle_time = (avg_cycle_time * 2 * last_live_memory) / penultimate_live_memory;
+ } else {
+ int degen_cycles = degenerated_cycles_in_a_row();
+ if (degen_cycles > 0) {
+ // If we've degenerated recently, we might be waiting too long between triggers so adjust trigger forward.
+ // TODO: Be more precise about how to scale when we've experienced recent degenerated GC. Existing code is a very
+ // rough approximation tuned with very limited workload observations.
+ avg_cycle_time += degen_cycles * avg_cycle_time;
+ }
+ }
+
double avg_alloc_rate = _allocation_rate.upper_bound(_margin_of_error_sd);
+ log_debug(gc)("%s: average GC time: %.2f ms, allocation rate: %.0f %s/s",
+ _generation->name(), avg_cycle_time * 1000, byte_size_in_proper_unit(avg_alloc_rate), proper_unit_for_byte_size(avg_alloc_rate));
+
if (avg_cycle_time > allocation_headroom / avg_alloc_rate) {
! if (avg_cycle_time > original_cycle_time) {
! log_debug(gc)("%s: average GC time adjusted from: %.2f ms to %.2f ms because upward trend in live memory retention",
+ _generation->name(), original_cycle_time, avg_cycle_time);
+ }
+
+ log_info(gc)("Trigger (%s): Average GC time (%.2f ms) is above the time for average allocation rate (%.0f %sB/s) to deplete free headroom (" SIZE_FORMAT "%s) (margin of error = %.2f)",
+ _generation->name(), avg_cycle_time * 1000,
byte_size_in_proper_unit(avg_alloc_rate), proper_unit_for_byte_size(avg_alloc_rate),
byte_size_in_proper_unit(allocation_headroom), proper_unit_for_byte_size(allocation_headroom),
_margin_of_error_sd);
log_info(gc, ergo)("Free headroom: " SIZE_FORMAT "%s (free) - " SIZE_FORMAT "%s (spike) - " SIZE_FORMAT "%s (penalties) = " SIZE_FORMAT "%s",
return true;
}
bool is_spiking = _allocation_rate.is_spiking(rate, _spike_threshold_sd);
if (is_spiking && avg_cycle_time > allocation_headroom / rate) {
! log_info(gc)("Trigger: Average GC time (%.2f ms) is above the time for instantaneous allocation rate (%.0f %sB/s) to deplete free headroom (" SIZE_FORMAT "%s) (spike threshold = %.2f)",
! avg_cycle_time * 1000,
byte_size_in_proper_unit(rate), proper_unit_for_byte_size(rate),
byte_size_in_proper_unit(allocation_headroom), proper_unit_for_byte_size(allocation_headroom),
_spike_threshold_sd);
_last_trigger = SPIKE;
return true;
}
return true;
}
bool is_spiking = _allocation_rate.is_spiking(rate, _spike_threshold_sd);
if (is_spiking && avg_cycle_time > allocation_headroom / rate) {
! log_info(gc)("Trigger (%s): Average GC time (%.2f ms) is above the time for instantaneous allocation rate (%.0f %sB/s) to deplete free headroom (" SIZE_FORMAT "%s) (spike threshold = %.2f)",
! _generation->name(), avg_cycle_time * 1000,
byte_size_in_proper_unit(rate), proper_unit_for_byte_size(rate),
byte_size_in_proper_unit(allocation_headroom), proper_unit_for_byte_size(allocation_headroom),
+
_spike_threshold_sd);
_last_trigger = SPIKE;
return true;
}
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