Fix Non-Cooperative Core Migration + Fix yieldWithCoreMigration + Improve Mutex Locking in ConditionalVariableWait

The case of a thread not being in the core queue during a non-cooperative core affinity change would break things as the thread was non-conditionally removed and inserted, this has been fixed by adding a check to see if the thread exists in the core's queue prior to migration. In addition, `yieldWithCoreMigration` was broken by the previous commit as the fallthrough was intentional and removing it cause core migration without a yield which led to breakage in certain circumstances. The mutex locking logic was also improved in `ConditionalVariableWait` to use atomics in a more effective manner with less atomic operations being performed overall.
This commit is contained in:
PixelyIon 2021-03-02 15:19:13 +05:30 committed by ◱ Mark
parent 0233916489
commit 0ea02f2d56
5 changed files with 47 additions and 39 deletions

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@ -171,7 +171,7 @@
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@ -120,6 +120,27 @@ namespace skyline::kernel {
}
}
void Scheduler::MigrateToIdealCore(const std::shared_ptr<type::KThread> &thread, CoreContext *&core, std::unique_lock<std::mutex> &lock) {
// We need to check if the thread was in it's resident core's queue
// If it was, we need to remove it from the queue
auto it{std::find(core->queue.begin(), core->queue.end(), thread)};
bool wasInserted{it != core->queue.end()};
if (wasInserted) {
it = core->queue.erase(it);
if (it == core->queue.begin() && it != core->queue.end())
(*it)->wakeCondition.notify_one();
}
lock.unlock();
thread->coreId = thread->idealCore;
if (wasInserted)
// We need to add the thread to the ideal core queue, if it was previously it's resident core's queue
InsertThread(thread);
core = &cores.at(thread->coreId);
lock = std::unique_lock(core->mutex);
}
void Scheduler::WaitSchedule(bool loadBalance) {
auto &thread{state.thread};
CoreContext *core{&cores.at(thread->coreId)};
@ -127,14 +148,7 @@ namespace skyline::kernel {
auto wakeFunction{[&]() {
if (!thread->affinityMask.test(thread->coreId)) [[unlikely]] {
lock.unlock();
RemoveThread();
thread->coreId = thread->idealCore;
InsertThread(thread);
core = &cores.at(thread->coreId);
lock = std::unique_lock(core->mutex);
MigrateToIdealCore(thread, core, lock);
}
return !core->queue.empty() && core->queue.front() == thread;
}};
@ -173,14 +187,7 @@ namespace skyline::kernel {
std::unique_lock lock(core->mutex);
if (thread->wakeCondition.wait_for(lock, timeout, [&]() {
if (!thread->affinityMask.test(thread->coreId)) [[unlikely]] {
lock.unlock();
RemoveThread();
thread->coreId = thread->idealCore;
InsertThread(thread);
core = &cores.at(thread->coreId);
lock = std::unique_lock(core->mutex);
MigrateToIdealCore(thread, core, lock);
}
return !core->queue.empty() && core->queue.front() == thread;
})) {
@ -212,8 +219,7 @@ namespace skyline::kernel {
auto &front{core.queue.front()};
if (front != thread)
front->wakeCondition.notify_one(); // If we aren't at the front of the queue, only then should we wake the thread at the front up
} else if (!thread->forceYield) {
[[unlikely]]
} else if (!thread->forceYield) [[unlikely]] {
throw exception("T{} called Rotate while not being in C{}'s queue", thread->id, thread->coreId);
}

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@ -57,6 +57,12 @@ namespace skyline {
std::mutex parkedMutex; //!< Synchronizes all operations on the queue of parked threads
std::list<std::shared_ptr<type::KThread>> parkedQueue; //!< A queue of threads which are parked and waiting on core migration
/**
* @brief Migrate a thread from it's resident core to it's ideal core
* @note This is used to handle non-cooperative core affinity mask changes where the resident core is not in it's new affinity mask
*/
void MigrateToIdealCore(const std::shared_ptr<type::KThread>& thread, CoreContext*& core, std::unique_lock<std::mutex>& lock);
public:
static constexpr std::chrono::milliseconds PreemptiveTimeslice{10}; //!< The duration of time a preemptive thread can run before yielding
inline static int YieldSignal{SIGRTMIN}; //!< The signal used to cause a yield in running threads

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@ -300,12 +300,12 @@ namespace skyline::kernel::svc {
} else {
switch (in) {
case yieldWithCoreMigration:
state.logger->Debug("svcSleepThread: Waking any appropriate parked threads");
state.logger->Debug("svcSleepThread: Waking any appropriate parked threads and yielding");
state.scheduler->WakeParkedThread();
break;
[[fallthrough]];
case yieldWithoutCoreMigration:
state.logger->Debug("svcSleepThread: Cooperative Yield");
if (in == yieldWithoutCoreMigration)
state.logger->Debug("svcSleepThread: Cooperative yield");
state.scheduler->Rotate();
state.scheduler->WaitSchedule();
break;
@ -710,7 +710,7 @@ namespace skyline::kernel::svc {
else if (result == result::InvalidCurrentMemory)
result = Result{}; // If the mutex value isn't expected then it's still successful
else if (result == result::InvalidHandle)
state.logger->Warn("svcArbitrateLock: 'ownerHandle' invalid: 0x{:X}", ownerHandle);
state.logger->Warn("svcArbitrateLock: 'ownerHandle' invalid: 0x{:X} (0x{:X})", ownerHandle, mutex);
state.ctx->gpr.w0 = result;
}

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@ -264,16 +264,14 @@ namespace skyline::kernel::type {
state.scheduler->WaitSchedule(false);
}
while (true) {
KHandle value{};
if (!__atomic_compare_exchange_n(mutex, &value, tag, false, __ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST))
while (MutexLock(mutex, value & ~HandleWaitersBit, tag) != Result{})
if ((value = __atomic_or_fetch(mutex, HandleWaitersBit, __ATOMIC_SEQ_CST)) == HandleWaitersBit)
if (__atomic_compare_exchange_n(mutex, &value, tag, false, __ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST))
break;
return {};
if (!(value & HandleWaitersBit))
if (!__atomic_compare_exchange_n(mutex, &value, value | HandleWaitersBit, false, __ATOMIC_SEQ_CST, __ATOMIC_RELAXED))
continue;
if (MutexLock(mutex, value & ~HandleWaitersBit, tag) == Result{})
return {};
}
}
void KProcess::ConditionalVariableSignal(u32 *key, i32 amount) {
@ -281,7 +279,6 @@ namespace skyline::kernel::type {
auto queue{syncWaiters.equal_range(key)};
auto it{queue.first};
if (queue.first != queue.second)
for (i32 waiterCount{amount}; it != queue.second && (amount <= 0 || waiterCount); it = syncWaiters.erase(it), waiterCount--)
state.scheduler->InsertThread(it->second);
@ -330,7 +327,6 @@ namespace skyline::kernel::type {
return result::InvalidState;
i32 waiterCount{amount};
if (queue.first != queue.second)
for (auto it{queue.first}; it != queue.second && (amount <= 0 || waiterCount); it = syncWaiters.erase(it), waiterCount--)
state.scheduler->InsertThread(it->second);