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More detailed instrumentation and simpler allocatable calculation

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This commit is contained in:
Kelvin Nilsen 2026-01-26 04:07:33 +00:00
parent ef654d3c75
commit e75b83ec29
2 changed files with 42 additions and 13 deletions
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46
src/hotspot/share/gc/shenandoah/heuristics/shenandoahAdaptiveHeuristics.cpp
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@ -149,24 +149,38 @@ void ShenandoahAdaptiveHeuristics::recalculate_trigger_threshold(size_t mutator_
size_t bytes_allocated_at_start_of_idle_span = _free_set->get_bytes_allocated_since_gc_start();
// make headroom adjustments
size_t headroom_adjustments = spike_headroom + penalties;
if (mutator_available >= headroom_adjustments) {
mutator_available -= headroom_adjustments;;
_headroom_adjustment = spike_headroom + penalties;
size_t adjusted_mutator_available;
if (mutator_available >= _headroom_adjustment) {
adjusted_mutator_available = mutator_available - _headroom_adjustment;
} else {
mutator_available = 0;
adjusted_mutator_available = 0;
}
assert(!_is_generational || !strcmp(_space_info->name(), "Young") || !strcmp(_space_info->name(), "Global"),
"Assumed young or global space, but got: %s", _space_info->name());
assert(_is_generational || !strcmp(_space_info->name(), ""), "Assumed global (unnamed) space, but got: %s", _space_info->name());
log_info(gc)("At start or resumption of idle gc span for %s, mutator available set to: " PROPERFMT
log_info(gc)("At start or resumption of idle gc span for %s, mutator available adjusted to: " PROPERFMT
" after adjusting for spike_headroom: " PROPERFMT " and penalties: " PROPERFMT,
_is_generational? _space_info->name(): "Global",
PROPERFMTARGS(mutator_available), PROPERFMTARGS(spike_headroom), PROPERFMTARGS(penalties));
PROPERFMTARGS(adjusted_mutator_available), PROPERFMTARGS(spike_headroom), PROPERFMTARGS(penalties));
_most_recent_headroom_at_start_of_idle = mutator_available;
_most_recent_headroom_at_start_of_idle = adjusted_mutator_available;
// _trigger_threshold is expressed in words
_trigger_threshold = (bytes_allocated_at_start_of_idle_span + mutator_available) / HeapWordSize;
_trigger_threshold = (bytes_allocated_at_start_of_idle_span + adjusted_mutator_available) / HeapWordSize;
#define KELVIN_DEBUG
#ifdef KELVIN_DEBUG
// _free_set->available() should match mutator_available
log_info(gc)("mutator_available: %zu, adjusted_mutator_available: %zu, _free_set->available(): %zu, "
"bytes_allocated_at_start: %zu, threshold: %zu",
mutator_available, adjusted_mutator_available, _free_set->available(), bytes_allocated_at_start_of_idle_span,
_trigger_threshold);
// Throughout idle span, available() should equal (allocatable() + spike_headroom + penalties)
size_t available = _free_set->available();
log_info(gc)(" available: %zu should equal allocatable: %zu + spike_headroom: %zu + penalties: %zu",
available, this->allocatable(available) * HeapWordSize, spike_headroom, penalties);
#endif
}
void ShenandoahAdaptiveHeuristics::start_idle_span() {
@ -545,9 +559,7 @@ bool ShenandoahAdaptiveHeuristics::should_start_gc() {
// log_info(gc)("AppendTrigger(first_rejected: %zu, rejected_count: %zu) @%.6f",
// first_rejected_trigger, rejected_trigger_count, ts);
#define AppendTriggerInfo(ts, cap, avail, alloced, mt, ls, aar, aw, act, pfagt, absls, \
#define ForceAppendTriggerInfo(ts, cap, avail, alloced, mt, ls, aar, aw, act, pfagt, absls, \
irwps, crba, ca, accel, pfgt, fpgt, attda, is, r, sr, sttda) \
if (rejected_trigger_count >= MaxRejectedTriggers) { \
first_rejected_trigger++; \
@ -584,9 +596,17 @@ bool ShenandoahAdaptiveHeuristics::should_start_gc() {
rejected_trigger_log[__j].spike_time_to_deplete_available = sttda; \
}
// We do not append trigger info for non-consequential sample periods
#define AppendTriggerInfo(ts, cap, avail, alloced, mt, ls, aar, aw, act, pfagt, absls, \
irwps, crba, ca, accel, pfgt, fpgt, attda, is, r, sr, sttda) \
if (((absls) > 0) || ((sr) > 0)) { \
ForceAppendTriggerInfo(ts, cap, avail, alloced, mt, ls, aar, aw, act, pfagt, absls, \
irwps, crba, ca, accel, pfgt, fpgt, attda, is, r, sr, sttda) \
}
#define DumpTriggerInfo(ts, cap, avail, alloced, mt, ls, aar, aw, act, pfagt, absls, \
irwps, crba, ca, accel, pfgt, fpgt, attda, is, r, sr, sttda) \
AppendTriggerInfo(ts, cap, avail, alloced, mt, ls, \
ForceAppendTriggerInfo(ts, cap, avail, alloced, mt, ls, \
aar, aw, act, pfagt, absls, irwps, crba, ca, accel, \
pfgt, fpgt, attda, is, r, sr, sttda); \
dumpTriggerInfo(first_rejected_trigger, rejected_trigger_count, rejected_trigger_log); \
@ -608,7 +628,7 @@ bool ShenandoahAdaptiveHeuristics::should_start_gc() {
double avg_cycle_time = 0;
double avg_alloc_rate = 0;
double now = get_most_recent_wake_time();
size_t allocatable_words = this->allocatable();
size_t allocatable_words = this->allocatable(available);
double predicted_future_accelerated_gc_time = 0.0;
size_t allocated_bytes_since_last_sample = 0;
double instantaneous_rate_words_per_second = 0.0;

9
src/hotspot/share/gc/shenandoah/heuristics/shenandoahAdaptiveHeuristics.hpp
View File

@ -183,12 +183,19 @@ public:
void adjust_margin_of_error(double amount);
void adjust_spike_threshold(double amount);
#ifdef KELVIN_DEPRECATE
// Returns number of words that can be allocated before we need to trigger next GC.
inline size_t allocatable() const {
size_t allocated_bytes = _free_set->get_bytes_allocated_since_gc_start();
size_t allocated_words = allocated_bytes / HeapWordSize;
return (allocated_words < _trigger_threshold)? _trigger_threshold - allocated_words: 0;
}
#endif
// Returns number of words that can be allocated before we need to trigger next GC, given available in bytes.
inline size_t allocatable(size_t available) const {
return (available > _headroom_adjustment)? (available - _headroom_adjustment) / HeapWordSize: 0;
}
protected:
ShenandoahAllocationRate _allocation_rate;
@ -232,6 +239,8 @@ protected:
double _previous_allocation_timestamp;
size_t _total_allocations_at_start_of_idle;
size_t _trigger_threshold;
// bytes of headroom at which we should trigger GC
size_t _headroom_adjustment;
// Keep track of GC_TIME_SAMPLE_SIZE most recent concurrent GC cycle times
uint _gc_time_first_sample_index;