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ladybird/Kernel/Scheduler.cpp
sin-ack 3f3f45580a Everywhere: Add sv suffix to strings relying on StringView(char const*) 
Each of these strings would previously rely on StringView's char const*
constructor overload, which would call __builtin_strlen on the string.
Since we now have operator ""sv, we can replace these with much simpler
versions. This opens the door to being able to remove
StringView(char const*).

No functional changes.
2022-07-12 23:11:35 +02:00

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/*
* Copyright (c) 2018-2021, 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>
// Remove this once SMP is stable and can be enabled by default
#define SCHEDULE_ON_ALL_PROCESSORS 0
namespace Kernel {
RecursiveSpinlock g_scheduler_lock;
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;
// 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)
{
if (Memory::s_mm_lock.is_locked_by_current_processor()) {
PANIC("In context switch while holding Memory::s_mm_lock");
}
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;
}
RefPtr<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 !SCHEDULE_ON_ALL_PROCESSORS
if (!Processor::is_bootstrap_processor())
return; // TODO: This prevents scheduling on other CPUs!
#endif
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();
#if SCHEDULE_ON_ALL_PROCESSORS
yield();
#else
if (Processor::current_id() == 0)
yield();
#endif
}
}
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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