8261496: Shenandoah: reconsider pacing updates memory ordering
Reviewed-by: rkennke, clanger
Backport-of: 4642730b057bfa37df740fc8d9e17bfb60e53447
diff --git a/src/hotspot/share/gc/shenandoah/shenandoahControlThread.cpp b/src/hotspot/share/gc/shenandoah/shenandoahControlThread.cpp
index 121631a..c198533 100644
--- a/src/hotspot/share/gc/shenandoah/shenandoahControlThread.cpp
+++ b/src/hotspot/share/gc/shenandoah/shenandoahControlThread.cpp
@@ -93,7 +93,7 @@
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<size_t>(0, &_allocs_seen);
+ size_t allocs_seen = Atomic::xchg<size_t>(0, &_allocs_seen, memory_order_relaxed);
// Check if we have seen a new target for soft max heap size.
bool soft_max_changed = check_soft_max_changed();
@@ -627,7 +627,7 @@
void ShenandoahControlThread::pacing_notify_alloc(size_t words) {
assert(ShenandoahPacing, "should only call when pacing is enabled");
- Atomic::add(words, &_allocs_seen);
+ Atomic::add(words, &_allocs_seen, memory_order_relaxed);
}
void ShenandoahControlThread::set_forced_counters_update(bool value) {
diff --git a/src/hotspot/share/gc/shenandoah/shenandoahPacer.cpp b/src/hotspot/share/gc/shenandoah/shenandoahPacer.cpp
index 1b96e6e..43da376 100644
--- a/src/hotspot/share/gc/shenandoah/shenandoahPacer.cpp
+++ b/src/hotspot/share/gc/shenandoah/shenandoahPacer.cpp
@@ -187,7 +187,7 @@
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((intptr_t)initial, &_budget);
+ Atomic::xchg((intptr_t)initial, &_budget, memory_order_relaxed);
Atomic::store(tax_rate, &_tax_rate);
Atomic::inc(&_epoch);
@@ -209,14 +209,14 @@
return false;
}
new_val = cur - tax;
- } while (Atomic::cmpxchg(new_val, &_budget, cur) != cur);
+ } while (Atomic::cmpxchg(new_val, &_budget, cur, 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;
}
diff --git a/src/hotspot/share/gc/shenandoah/shenandoahPacer.inline.hpp b/src/hotspot/share/gc/shenandoah/shenandoahPacer.inline.hpp
index 2db3df5..c98930e 100644
--- a/src/hotspot/share/gc/shenandoah/shenandoahPacer.inline.hpp
+++ b/src/hotspot/share/gc/shenandoah/shenandoahPacer.inline.hpp
@@ -53,13 +53,13 @@
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((intptr_t)words, &_progress);
+ Atomic::add((intptr_t)words, &_progress, 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(inc, &_budget);
+ intptr_t new_budget = Atomic::add(inc, &_budget, memory_order_relaxed);
// Was the budget replenished beyond zero? Then all pacing claims
// are satisfied, notify the waiters. Avoid taking any locks here,
