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ladybird/Kernel/Scheduler.cpp
Andreas Kling a3b2b20782 Kernel: Remove global MM lock in favor of SpinlockProtected 
Globally shared MemoryManager state is now kept in a GlobalData struct
and wrapped in SpinlockProtected.

A small set of members are left outside the GlobalData struct as they
are only set during boot initialization, and then remain constant.
This allows us to access those members without taking any locks.
2022-08-26 01:04:51 +02:00

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/*
* Copyright (c) 2018-2022, Andreas Kling <kling@serenityos.org>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#include <AK/BuiltinWrappers.h>
#include <AK/ScopeGuard.h>
#include <AK/Singleton.h>
#include <AK/Time.h>
#include <Kernel/Arch/InterruptDisabler.h>
#include <Kernel/Arch/x86/TrapFrame.h>
#include <Kernel/Debug.h>
#include <Kernel/Panic.h>
#include <Kernel/PerformanceManager.h>
#include <Kernel/Process.h>
#include <Kernel/RTC.h>
#include <Kernel/Scheduler.h>
#include <Kernel/Sections.h>
#include <Kernel/Time/TimeManagement.h>
#include <Kernel/kstdio.h>
namespace Kernel {
RecursiveSpinlock g_scheduler_lock { LockRank::None };
static u32 time_slice_for(Thread const& thread)
{
// One time slice unit == 4ms (assuming 250 ticks/second)
if (thread.is_idle_thread())
return 1;
return 2;
}
READONLY_AFTER_INIT Thread* g_finalizer;
READONLY_AFTER_INIT WaitQueue* g_finalizer_wait_queue;
Atomic<bool> g_finalizer_has_work { false };
READONLY_AFTER_INIT static Process* s_colonel_process;
struct ThreadReadyQueue {
IntrusiveList<&Thread::m_ready_queue_node> thread_list;
};
struct ThreadReadyQueues {
u32 mask {};
static constexpr size_t count = sizeof(mask) * 8;
Array<ThreadReadyQueue, count> queues;
};
static Singleton<SpinlockProtected<ThreadReadyQueues>> g_ready_queues;
static SpinlockProtected<TotalTimeScheduled> g_total_time_scheduled { LockRank::None };
// The Scheduler::current_time function provides a current time for scheduling purposes,
// which may not necessarily relate to wall time
u64 (*Scheduler::current_time)();
static void dump_thread_list(bool = false);
static inline u32 thread_priority_to_priority_index(u32 thread_priority)
{
// Converts the priority in the range of THREAD_PRIORITY_MIN...THREAD_PRIORITY_MAX
// to a index into g_ready_queues where 0 is the highest priority bucket
VERIFY(thread_priority >= THREAD_PRIORITY_MIN && thread_priority <= THREAD_PRIORITY_MAX);
constexpr u32 thread_priority_count = THREAD_PRIORITY_MAX - THREAD_PRIORITY_MIN + 1;
static_assert(thread_priority_count > 0);
auto priority_bucket = ((thread_priority_count - (thread_priority - THREAD_PRIORITY_MIN)) / thread_priority_count) * (ThreadReadyQueues::count - 1);
VERIFY(priority_bucket < ThreadReadyQueues::count);
return priority_bucket;
}
Thread& Scheduler::pull_next_runnable_thread()
{
auto affinity_mask = 1u << Processor::current_id();
return g_ready_queues->with([&](auto& ready_queues) -> Thread& {
auto priority_mask = ready_queues.mask;
while (priority_mask != 0) {
auto priority = bit_scan_forward(priority_mask);
VERIFY(priority > 0);
auto& ready_queue = ready_queues.queues[--priority];
for (auto& thread : ready_queue.thread_list) {
VERIFY(thread.m_runnable_priority == (int)priority);
if (thread.is_active())
continue;
if (!(thread.affinity() & affinity_mask))
continue;
thread.m_runnable_priority = -1;
ready_queue.thread_list.remove(thread);
if (ready_queue.thread_list.is_empty())
ready_queues.mask &= ~(1u << priority);
// Mark it as active because we are using this thread. This is similar
// to comparing it with Processor::current_thread, but when there are
// multiple processors there's no easy way to check whether the thread
// is actually still needed. This prevents accidental finalization when
// a thread is no longer in Running state, but running on another core.
// We need to mark it active here so that this thread won't be
// scheduled on another core if it were to be queued before actually
// switching to it.
// FIXME: Figure out a better way maybe?
thread.set_active(true);
return thread;
}
priority_mask &= ~(1u << priority);
}
return *Processor::idle_thread();
});
}
Thread* Scheduler::peek_next_runnable_thread()
{
auto affinity_mask = 1u << Processor::current_id();
return g_ready_queues->with([&](auto& ready_queues) -> Thread* {
auto priority_mask = ready_queues.mask;
while (priority_mask != 0) {
auto priority = bit_scan_forward(priority_mask);
VERIFY(priority > 0);
auto& ready_queue = ready_queues.queues[--priority];
for (auto& thread : ready_queue.thread_list) {
VERIFY(thread.m_runnable_priority == (int)priority);
if (thread.is_active())
continue;
if (!(thread.affinity() & affinity_mask))
continue;
return &thread;
}
priority_mask &= ~(1u << priority);
}
// Unlike in pull_next_runnable_thread() we don't want to fall back to
// the idle thread. We just want to see if we have any other thread ready
// to be scheduled.
return nullptr;
});
}
bool Scheduler::dequeue_runnable_thread(Thread& thread, bool check_affinity)
{
if (thread.is_idle_thread())
return true;
return g_ready_queues->with([&](auto& ready_queues) {
auto priority = thread.m_runnable_priority;
if (priority < 0) {
VERIFY(!thread.m_ready_queue_node.is_in_list());
return false;
}
if (check_affinity && !(thread.affinity() & (1 << Processor::current_id())))
return false;
VERIFY(ready_queues.mask & (1u << priority));
auto& ready_queue = ready_queues.queues[priority];
thread.m_runnable_priority = -1;
ready_queue.thread_list.remove(thread);
if (ready_queue.thread_list.is_empty())
ready_queues.mask &= ~(1u << priority);
return true;
});
}
void Scheduler::enqueue_runnable_thread(Thread& thread)
{
VERIFY(g_scheduler_lock.is_locked_by_current_processor());
if (thread.is_idle_thread())
return;
auto priority = thread_priority_to_priority_index(thread.priority());
g_ready_queues->with([&](auto& ready_queues) {
VERIFY(thread.m_runnable_priority < 0);
thread.m_runnable_priority = (int)priority;
VERIFY(!thread.m_ready_queue_node.is_in_list());
auto& ready_queue = ready_queues.queues[priority];
bool was_empty = ready_queue.thread_list.is_empty();
ready_queue.thread_list.append(thread);
if (was_empty)
ready_queues.mask |= (1u << priority);
});
}
UNMAP_AFTER_INIT void Scheduler::start()
{
VERIFY_INTERRUPTS_DISABLED();
// We need to acquire our scheduler lock, which will be released
// by the idle thread once control transferred there
g_scheduler_lock.lock();
auto& processor = Processor::current();
VERIFY(processor.is_initialized());
auto& idle_thread = *Processor::idle_thread();
VERIFY(processor.current_thread() == &idle_thread);
idle_thread.set_ticks_left(time_slice_for(idle_thread));
idle_thread.did_schedule();
idle_thread.set_initialized(true);
processor.init_context(idle_thread, false);
idle_thread.set_state(Thread::State::Running);
VERIFY(idle_thread.affinity() == (1u << processor.id()));
processor.initialize_context_switching(idle_thread);
VERIFY_NOT_REACHED();
}
void Scheduler::pick_next()
{
VERIFY_INTERRUPTS_DISABLED();
// Set the in_scheduler flag before acquiring the spinlock. This
// prevents a recursive call into Scheduler::invoke_async upon
// leaving the scheduler lock.
ScopedCritical critical;
Processor::set_current_in_scheduler(true);
ScopeGuard guard(
[]() {
// We may be on a different processor after we got switched
// back to this thread!
VERIFY(Processor::current_in_scheduler());
Processor::set_current_in_scheduler(false);
});
SpinlockLocker lock(g_scheduler_lock);
if constexpr (SCHEDULER_RUNNABLE_DEBUG) {
dump_thread_list();
}
auto& thread_to_schedule = pull_next_runnable_thread();
if constexpr (SCHEDULER_DEBUG) {
dbgln("Scheduler[{}]: Switch to {} @ {:#04x}:{:p}",
Processor::current_id(),
thread_to_schedule,
thread_to_schedule.regs().cs, thread_to_schedule.regs().ip());
}
// We need to leave our first critical section before switching context,
// but since we're still holding the scheduler lock we're still in a critical section
critical.leave();
thread_to_schedule.set_ticks_left(time_slice_for(thread_to_schedule));
context_switch(&thread_to_schedule);
}
void Scheduler::yield()
{
InterruptDisabler disabler;
auto const* current_thread = Thread::current();
dbgln_if(SCHEDULER_DEBUG, "Scheduler[{}]: yielding thread {} in_irq={}", Processor::current_id(), *current_thread, Processor::current_in_irq());
VERIFY(current_thread != nullptr);
if (Processor::current_in_irq() || Processor::in_critical()) {
// If we're handling an IRQ we can't switch context, or we're in
// a critical section where we don't want to switch contexts, then
// delay until exiting the trap or critical section
Processor::current().invoke_scheduler_async();
return;
}
Scheduler::pick_next();
}
void Scheduler::context_switch(Thread* thread)
{
thread->did_schedule();
auto* from_thread = Thread::current();
VERIFY(from_thread);
if (from_thread == thread)
return;
// If the last process hasn't blocked (still marked as running),
// mark it as runnable for the next round.
if (from_thread->state() == Thread::State::Running)
from_thread->set_state(Thread::State::Runnable);
#ifdef LOG_EVERY_CONTEXT_SWITCH
auto const msg = "Scheduler[{}]: {} -> {} [prio={}] {:#04x}:{:p}";
dbgln(msg,
Processor::current_id(), from_thread->tid().value(),
thread->tid().value(), thread->priority(), thread->regs().cs, thread->regs().ip());
#endif
auto& proc = Processor::current();
if (!thread->is_initialized()) {
proc.init_context(*thread, false);
thread->set_initialized(true);
}
thread->set_state(Thread::State::Running);
PerformanceManager::add_context_switch_perf_event(*from_thread, *thread);
proc.switch_context(from_thread, thread);
// NOTE: from_thread at this point reflects the thread we were
// switched from, and thread reflects Thread::current()
enter_current(*from_thread);
VERIFY(thread == Thread::current());
{
SpinlockLocker lock(thread->get_lock());
thread->dispatch_one_pending_signal();
}
}
void Scheduler::enter_current(Thread& prev_thread)
{
VERIFY(g_scheduler_lock.is_locked_by_current_processor());
// We already recorded the scheduled time when entering the trap, so this merely accounts for the kernel time since then
auto scheduler_time = Scheduler::current_time();
prev_thread.update_time_scheduled(scheduler_time, true, true);
auto* current_thread = Thread::current();
current_thread->update_time_scheduled(scheduler_time, true, false);
// NOTE: When doing an exec(), we will context switch from and to the same thread!
// In that case, we must not mark the previous thread as inactive.
if (&prev_thread != current_thread)
prev_thread.set_active(false);
if (prev_thread.state() == Thread::State::Dying) {
// If the thread we switched from is marked as dying, then notify
// the finalizer. Note that as soon as we leave the scheduler lock
// the finalizer may free from_thread!
notify_finalizer();
}
}
void Scheduler::leave_on_first_switch(u32 flags)
{
// This is called when a thread is switched into for the first time.
// At this point, enter_current has already be called, but because
// Scheduler::context_switch is not in the call stack we need to
// clean up and release locks manually here
g_scheduler_lock.unlock(flags);
VERIFY(Processor::current_in_scheduler());
Processor::set_current_in_scheduler(false);
}
void Scheduler::prepare_after_exec()
{
// This is called after exec() when doing a context "switch" into
// the new process. This is called from Processor::assume_context
VERIFY(g_scheduler_lock.is_locked_by_current_processor());
VERIFY(!Processor::current_in_scheduler());
Processor::set_current_in_scheduler(true);
}
void Scheduler::prepare_for_idle_loop()
{
// This is called when the CPU finished setting up the idle loop
// and is about to run it. We need to acquire the scheduler lock
VERIFY(!g_scheduler_lock.is_locked_by_current_processor());
g_scheduler_lock.lock();
VERIFY(!Processor::current_in_scheduler());
Processor::set_current_in_scheduler(true);
}
Process* Scheduler::colonel()
{
VERIFY(s_colonel_process);
return s_colonel_process;
}
static u64 current_time_tsc()
{
return read_tsc();
}
static u64 current_time_monotonic()
{
// We always need a precise timestamp here, we cannot rely on a coarse timestamp
return (u64)TimeManagement::the().monotonic_time(TimePrecision::Precise).to_nanoseconds();
}
UNMAP_AFTER_INIT void Scheduler::initialize()
{
VERIFY(Processor::is_initialized()); // sanity check
// Figure out a good scheduling time source
if (Processor::current().has_feature(CPUFeature::TSC)) {
// TODO: only use if TSC is running at a constant frequency?
current_time = current_time_tsc;
} else {
// TODO: Using HPET is rather slow, can we use any other time source that may be faster?
current_time = current_time_monotonic;
}
LockRefPtr<Thread> idle_thread;
g_finalizer_wait_queue = new WaitQueue;
g_finalizer_has_work.store(false, AK::MemoryOrder::memory_order_release);
s_colonel_process = Process::create_kernel_process(idle_thread, KString::must_create("colonel"sv), idle_loop, nullptr, 1, Process::RegisterProcess::No).leak_ref();
VERIFY(s_colonel_process);
VERIFY(idle_thread);
idle_thread->set_priority(THREAD_PRIORITY_MIN);
idle_thread->set_name(KString::must_create("Idle Task #0"sv));
set_idle_thread(idle_thread);
}
UNMAP_AFTER_INIT void Scheduler::set_idle_thread(Thread* idle_thread)
{
idle_thread->set_idle_thread();
Processor::current().set_idle_thread(*idle_thread);
Processor::set_current_thread(*idle_thread);
}
UNMAP_AFTER_INIT Thread* Scheduler::create_ap_idle_thread(u32 cpu)
{
VERIFY(cpu != 0);
// This function is called on the bsp, but creates an idle thread for another AP
VERIFY(Processor::is_bootstrap_processor());
VERIFY(s_colonel_process);
Thread* idle_thread = s_colonel_process->create_kernel_thread(idle_loop, nullptr, THREAD_PRIORITY_MIN, MUST(KString::formatted("idle thread #{}", cpu)), 1 << cpu, false);
VERIFY(idle_thread);
return idle_thread;
}
void Scheduler::add_time_scheduled(u64 time_to_add, bool is_kernel)
{
g_total_time_scheduled.with([&](auto& total_time_scheduled) {
total_time_scheduled.total += time_to_add;
if (is_kernel)
total_time_scheduled.total_kernel += time_to_add;
});
}
void Scheduler::timer_tick(RegisterState const& regs)
{
VERIFY_INTERRUPTS_DISABLED();
VERIFY(Processor::current_in_irq());
auto* current_thread = Processor::current_thread();
if (!current_thread)
return;
// Sanity checks
VERIFY(current_thread->current_trap());
VERIFY(current_thread->current_trap()->regs == &regs);
if (current_thread->process().is_kernel_process()) {
// Because the previous mode when entering/exiting kernel threads never changes
// we never update the time scheduled. So we need to update it manually on the
// timer interrupt
current_thread->update_time_scheduled(current_time(), true, false);
}
if (current_thread->previous_mode() == Thread::PreviousMode::UserMode && current_thread->should_die() && !current_thread->is_blocked()) {
SpinlockLocker scheduler_lock(g_scheduler_lock);
dbgln_if(SCHEDULER_DEBUG, "Scheduler[{}]: Terminating user mode thread {}", Processor::current_id(), *current_thread);
current_thread->set_state(Thread::State::Dying);
Processor::current().invoke_scheduler_async();
return;
}
if (current_thread->tick())
return;
if (!current_thread->is_idle_thread() && !peek_next_runnable_thread()) {
// If no other thread is ready to be scheduled we don't need to
// switch to the idle thread. Just give the current thread another
// time slice and let it run!
current_thread->set_ticks_left(time_slice_for(*current_thread));
current_thread->did_schedule();
dbgln_if(SCHEDULER_DEBUG, "Scheduler[{}]: No other threads ready, give {} another timeslice", Processor::current_id(), *current_thread);
return;
}
VERIFY_INTERRUPTS_DISABLED();
VERIFY(Processor::current_in_irq());
Processor::current().invoke_scheduler_async();
}
void Scheduler::invoke_async()
{
VERIFY_INTERRUPTS_DISABLED();
VERIFY(!Processor::current_in_irq());
// Since this function is called when leaving critical sections (such
// as a Spinlock), we need to check if we're not already doing this
// to prevent recursion
if (!Processor::current_in_scheduler())
pick_next();
}
void Scheduler::notify_finalizer()
{
if (!g_finalizer_has_work.exchange(true, AK::MemoryOrder::memory_order_acq_rel))
g_finalizer_wait_queue->wake_all();
}
void Scheduler::idle_loop(void*)
{
auto& proc = Processor::current();
dbgln("Scheduler[{}]: idle loop running", proc.id());
VERIFY(are_interrupts_enabled());
for (;;) {
proc.idle_begin();
asm("hlt");
proc.idle_end();
VERIFY_INTERRUPTS_ENABLED();
yield();
}
}
void Scheduler::dump_scheduler_state(bool with_stack_traces)
{
dump_thread_list(with_stack_traces);
}
bool Scheduler::is_initialized()
{
// The scheduler is initialized iff the idle thread exists
return Processor::idle_thread() != nullptr;
}
TotalTimeScheduled Scheduler::get_total_time_scheduled()
{
return g_total_time_scheduled.with([&](auto& total_time_scheduled) { return total_time_scheduled; });
}
void dump_thread_list(bool with_stack_traces)
{
dbgln("Scheduler thread list for processor {}:", Processor::current_id());
auto get_cs = [](Thread& thread) -> u16 {
if (!thread.current_trap())
return thread.regs().cs;
return thread.get_register_dump_from_stack().cs;
};
auto get_eip = [](Thread& thread) -> u32 {
if (!thread.current_trap())
return thread.regs().ip();
return thread.get_register_dump_from_stack().ip();
};
Thread::for_each([&](Thread& thread) {
switch (thread.state()) {
case Thread::State::Dying:
dmesgln(" {:14} {:30} @ {:04x}:{:08x} Finalizable: {}, (nsched: {})",
thread.state_string(),
thread,
get_cs(thread),
get_eip(thread),
thread.is_finalizable(),
thread.times_scheduled());
break;
default:
dmesgln(" {:14} Pr:{:2} {:30} @ {:04x}:{:08x} (nsched: {})",
thread.state_string(),
thread.priority(),
thread,
get_cs(thread),
get_eip(thread),
thread.times_scheduled());
break;
}
if (with_stack_traces) {
auto trace_or_error = thread.backtrace();
if (!trace_or_error.is_error()) {
auto trace = trace_or_error.release_value();
dbgln("Backtrace:");
kernelputstr(trace->characters(), trace->length());
}
}
return IterationDecision::Continue;
});
}
}
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