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Recalculate highest-priority waiters during cvar/address signaling

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`SignalToAddress`/`ConditionVariableSignal` need to wake waiters in priority order, while threads are inserted in order this doesn't remain the case as priority updates don't reinsert the thread into `syncWaiters`. 

It was determined that reinsertion into `syncWaiters` would be fairly complex due to locking the `syncWaitersMutex` with the thread's mutexes. To avoid this, this commit instead sorts waiters by priority at signal time to always wake threads in the right order.
This commit is contained in:
PixelyIon 2022-11-28 23:25:03 +05:30 committed by Mark Collins
parent 626008d8e2
commit 7f7352ed59
1 changed files with 21 additions and 5 deletions
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26
app/src/main/cpp/skyline/kernel/types/KProcess.cpp
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@ -330,15 +330,16 @@ namespace skyline::kernel::type {
auto queue{syncWaiters.equal_range(key)};
if (queue.first != queue.second) {
// If we found a thread then we need to remove it from the queue
thread = queue.first->second;
// If threads are waiting on us still then we need to remove the highest priority thread from the queue
auto it{std::min_element(queue.first, queue.second, [](const SyncWaiters::value_type &lhs, const SyncWaiters::value_type &rhs) { return lhs.second->priority < rhs.second->priority; })};
thread = it->second;
conditionVariable = thread->waitConditionVariable;
#ifndef NDEBUG
if (conditionVariable != key)
Logger::Warn("Condition variable mismatch: 0x{:X} != 0x{:X}", conditionVariable, key);
#endif
syncWaiters.erase(queue.first);
syncWaiters.erase(it);
waiterCount--;
} else if (queue.first == queue.second) {
// If we didn't find a thread then we need to clear the boolean flag denoting that there are no more threads waiting on this conditional variable
@ -488,8 +489,23 @@ namespace skyline::kernel::type {
}
i32 waiterCount{amount};
for (auto it{queue.first}; it != queue.second && (amount <= 0 || waiterCount); it = syncWaiters.erase(it), waiterCount--)
state.scheduler->InsertThread(it->second);
boost::container::small_vector<SyncWaiters::iterator, 10> orderedThreads;
for (auto it{queue.first}; it != queue.second; it++) {
// While threads should generally be inserted in priority order, they may not always be due to the way the kernel handles priority updates
// As a result, we need to create a second list of threads ordered by priority to ensure that we wake up the highest priority threads first
auto thread{it->second};
orderedThreads.insert(std::upper_bound(orderedThreads.begin(), orderedThreads.end(), thread->priority.load(), [](const i8 priority, const SyncWaiters::iterator &it) { return it->second->priority > priority; }), it);
}
for (auto &it : orderedThreads) {
auto thread{it->second};
syncWaiters.erase(it);
state.scheduler->InsertThread(thread);
if (--waiterCount == 0 && amount > 0)
break;
}
return {};
}