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8261496: Shenandoah: reconsider pacing updates memory ordering
Reviewed-by: zgu
  • Loading branch information
shipilev committed Feb 15, 2021
1 parent 7c93159 commit 4642730b057bfa37df740fc8d9e17bfb60e53447
@@ -100,7 +100,7 @@ void ShenandoahControlThread::run_service() {
bool implicit_gc_requested = _gc_requested.is_set() && !is_explicit_gc(_requested_gc_cause);

// This control loop iteration have seen this much allocations.
size_t allocs_seen = Atomic::xchg(&_allocs_seen, (size_t)0);
size_t allocs_seen = Atomic::xchg(&_allocs_seen, (size_t)0, memory_order_relaxed);

// Check if we have seen a new target for soft max heap size.
bool soft_max_changed = check_soft_max_changed();
@@ -595,7 +595,7 @@ void ShenandoahControlThread::notify_heap_changed() {

void ShenandoahControlThread::pacing_notify_alloc(size_t words) {
assert(ShenandoahPacing, "should only call when pacing is enabled");
Atomic::add(&_allocs_seen, words);
Atomic::add(&_allocs_seen, words, memory_order_relaxed);
}

void ShenandoahControlThread::set_forced_counters_update(bool value) {
@@ -179,7 +179,7 @@ size_t ShenandoahPacer::update_and_get_progress_history() {
void ShenandoahPacer::restart_with(size_t non_taxable_bytes, double tax_rate) {
size_t initial = (size_t)(non_taxable_bytes * tax_rate) >> LogHeapWordSize;
STATIC_ASSERT(sizeof(size_t) <= sizeof(intptr_t));
Atomic::xchg(&_budget, (intptr_t)initial);
Atomic::xchg(&_budget, (intptr_t)initial, memory_order_relaxed);
Atomic::store(&_tax_rate, tax_rate);
Atomic::inc(&_epoch);

@@ -201,14 +201,14 @@ bool ShenandoahPacer::claim_for_alloc(size_t words, bool force) {
return false;
}
new_val = cur - tax;
} while (Atomic::cmpxchg(&_budget, cur, new_val) != cur);
} while (Atomic::cmpxchg(&_budget, cur, new_val, memory_order_relaxed) != cur);
return true;
}

void ShenandoahPacer::unpace_for_alloc(intptr_t epoch, size_t words) {
assert(ShenandoahPacing, "Only be here when pacing is enabled");

if (_epoch != epoch) {
if (Atomic::load(&_epoch) != epoch) {
// Stale ticket, no need to unpace.
return;
}
@@ -53,13 +53,13 @@ inline void ShenandoahPacer::report_internal(size_t words) {
inline void ShenandoahPacer::report_progress_internal(size_t words) {
assert(ShenandoahPacing, "Only be here when pacing is enabled");
STATIC_ASSERT(sizeof(size_t) <= sizeof(intptr_t));
Atomic::add(&_progress, (intptr_t)words);
Atomic::add(&_progress, (intptr_t)words, memory_order_relaxed);
}

inline void ShenandoahPacer::add_budget(size_t words) {
STATIC_ASSERT(sizeof(size_t) <= sizeof(intptr_t));
intptr_t inc = (intptr_t) words;
intptr_t new_budget = Atomic::add(&_budget, inc);
intptr_t new_budget = Atomic::add(&_budget, inc, memory_order_relaxed);

// Was the budget replenished beyond zero? Then all pacing claims
// are satisfied, notify the waiters. Avoid taking any locks here,

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