Commit e9750cb8 authored by Gabriel Charette's avatar Gabriel Charette Committed by Commit Bot

Preempt ConcurrentMarking tasks instead of merely pausing in PauseScope.

Follow-up to https://chromium-review.googlesource.com/c/v8/v8/+/924867

This is the core goal of the initial CL @
https://chromium-review.googlesource.com/c/v8/v8/+/922103
which was since split into multiple to diagnose a bots-only failure.

Bug: chromium:812178
Change-Id: I4c4e0b517737e020862917bd89fa6ce38244e597
Reviewed-on: https://chromium-review.googlesource.com/924031
Commit-Queue: Gabriel Charette <gab@chromium.org>
Reviewed-by: 's avatarUlan Degenbaev <ulan@chromium.org>
Reviewed-by: 's avatarMichael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#51356}
parent a8f68c20
......@@ -436,13 +436,8 @@ void ConcurrentMarking::Run(int task_id, TaskState* task_state) {
GCTracer::BackgroundScope::MC_BACKGROUND_MARKING);
size_t kBytesUntilInterruptCheck = 64 * KB;
int kObjectsUntilInterrupCheck = 1000;
LiveBytesMap* live_bytes = nullptr;
{
base::LockGuard<base::Mutex> guard(&task_state->lock);
live_bytes = &task_state->live_bytes;
}
ConcurrentMarkingVisitor visitor(shared_, bailout_, live_bytes, weak_objects_,
task_id);
ConcurrentMarkingVisitor visitor(shared_, bailout_, &task_state->live_bytes,
weak_objects_, task_id);
double time_ms;
size_t marked_bytes = 0;
if (FLAG_trace_concurrent_marking) {
......@@ -451,8 +446,7 @@ void ConcurrentMarking::Run(int task_id, TaskState* task_state) {
}
{
TimedScope scope(&time_ms);
{
base::LockGuard<base::Mutex> guard(&task_state->lock);
bool done = false;
while (!done) {
size_t current_marked_bytes = 0;
......@@ -478,21 +472,15 @@ void ConcurrentMarking::Run(int task_id, TaskState* task_state) {
marked_bytes += current_marked_bytes;
base::AsAtomicWord::Relaxed_Store<size_t>(&task_state->marked_bytes,
marked_bytes);
if (task_state->interrupt_request.Value()) {
TRACE_EVENT0(TRACE_DISABLED_BY_DEFAULT("v8.gc"),
"ConcurrentMarking::Run Paused");
task_state->interrupt_condition.Wait(&task_state->lock);
} else if (task_state->preemption_request.Value()) {
if (task_state->preemption_request.Value()) {
TRACE_EVENT0(TRACE_DISABLED_BY_DEFAULT("v8.gc"),
"ConcurrentMarking::Run Preempted");
break;
}
}
// The lock is also required to synchronize with worklist update after
// young generation GC.
bailout_->FlushToGlobal(task_id);
on_hold_->FlushToGlobal(task_id);
}
weak_objects_->weak_cells.FlushToGlobal(task_id);
weak_objects_->transition_arrays.FlushToGlobal(task_id);
base::AsAtomicWord::Relaxed_Store<size_t>(&task_state->marked_bytes, 0);
......@@ -534,7 +522,6 @@ void ConcurrentMarking::ScheduleTasks() {
"Scheduling concurrent marking task %d\n", i);
}
task_state_[i].preemption_request.SetValue(false);
task_state_[i].interrupt_request.SetValue(false);
is_pending_[i] = true;
++pending_task_count_;
Task* task = new Task(heap_->isolate(), this, &task_state_[i], i);
......@@ -623,23 +610,12 @@ size_t ConcurrentMarking::TotalMarkedBytes() {
ConcurrentMarking::PauseScope::PauseScope(ConcurrentMarking* concurrent_marking)
: concurrent_marking_(concurrent_marking) {
if (!FLAG_concurrent_marking) return;
// Request task_state for all tasks.
for (int i = 1; i <= kMaxTasks; i++) {
concurrent_marking_->task_state_[i].interrupt_request.SetValue(true);
}
// Now take a lock to ensure that the tasks are waiting.
for (int i = 1; i <= kMaxTasks; i++) {
concurrent_marking_->task_state_[i].lock.Lock();
}
concurrent_marking_->Stop(ConcurrentMarking::StopRequest::PREEMPT_TASKS);
}
ConcurrentMarking::PauseScope::~PauseScope() {
if (!FLAG_concurrent_marking) return;
for (int i = kMaxTasks; i >= 1; i--) {
concurrent_marking_->task_state_[i].interrupt_request.SetValue(false);
concurrent_marking_->task_state_[i].interrupt_condition.NotifyAll();
concurrent_marking_->task_state_[i].lock.Unlock();
}
concurrent_marking_->RescheduleTasksIfNeeded();
}
} // namespace internal
......
......@@ -30,7 +30,8 @@ using LiveBytesMap =
class ConcurrentMarking {
public:
// When the scope is entered, the concurrent marking tasks
// are paused and are not looking at the heap objects.
// are preempted and are not looking at the heap objects, concurrent marking
// is resumed when the scope is exited.
class PauseScope {
public:
explicit PauseScope(ConcurrentMarking* concurrent_marking);
......@@ -81,16 +82,6 @@ class ConcurrentMarking {
// marker to give up the worker thread.
base::AtomicValue<bool> preemption_request;
// When the concurrent marking task has this lock, then objects in the
// heap are guaranteed to not move.
base::Mutex lock;
// The main thread sets this flag to true, when it wants the concurrent
// maker to give up the lock.
base::AtomicValue<bool> interrupt_request;
// The concurrent marker waits on this condition until the request
// flag is cleared by the main thread.
base::ConditionVariable interrupt_condition;
LiveBytesMap live_bytes;
size_t marked_bytes = 0;
char cache_line_padding[64];
......
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