abdd5aa08a
This patch introduces three separate thread queues, one for each thread priority available to userspace (Low, Normal and High.) Each queue operates in a round-robin fashion, but we now always prefer to schedule the highest priority thread that currently wants to run. There are tons of tweaks and improvements that we can and should make to this mechanism, but I think this is a step in the right direction. This makes WindowServer significantly more responsive while one of its clients is burning CPU. :^)
642 lines
20 KiB
C++
642 lines
20 KiB
C++
#include <AK/TemporaryChange.h>
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#include <Kernel/Arch/i386/PIT.h>
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#include <Kernel/FileSystem/FileDescription.h>
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#include <Kernel/Process.h>
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#include <Kernel/Profiling.h>
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#include <Kernel/RTC.h>
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#include <Kernel/Scheduler.h>
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//#define LOG_EVERY_CONTEXT_SWITCH
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//#define SCHEDULER_DEBUG
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//#define SCHEDULER_RUNNABLE_DEBUG
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SchedulerData* g_scheduler_data;
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void Scheduler::init_thread(Thread& thread)
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{
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g_scheduler_data->m_nonrunnable_threads.append(thread);
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}
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void Scheduler::update_state_for_thread(Thread& thread)
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{
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ASSERT_INTERRUPTS_DISABLED();
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auto& list = g_scheduler_data->thread_list_for_state_and_priority(thread.state(), thread.priority());
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if (list.contains(thread))
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return;
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list.append(thread);
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}
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template<typename Callback>
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static inline IterationDecision for_each_runnable_with_priority(ThreadPriority priority, Callback callback)
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{
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ASSERT_INTERRUPTS_DISABLED();
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auto& tl = g_scheduler_data->m_runnable_threads[(u8)priority - (u8)ThreadPriority::First];
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for (auto it = tl.begin(); it != tl.end();) {
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auto& thread = *it;
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it = ++it;
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if (callback(thread) == IterationDecision::Break)
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return IterationDecision::Break;
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}
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return IterationDecision::Continue;
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}
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static u32 time_slice_for(ThreadPriority priority)
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{
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// One time slice unit == 1ms
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switch (priority) {
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case ThreadPriority::High:
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return 20;
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case ThreadPriority::Normal:
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return 15;
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case ThreadPriority::Low:
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return 5;
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case ThreadPriority::Idle:
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return 1;
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}
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ASSERT_NOT_REACHED();
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}
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Thread* current;
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Thread* g_last_fpu_thread;
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Thread* g_finalizer;
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Thread* g_colonel;
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WaitQueue* g_finalizer_wait_queue;
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static Process* s_colonel_process;
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u64 g_uptime;
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struct TaskRedirectionData {
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u16 selector;
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TSS32 tss;
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};
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static TaskRedirectionData s_redirection;
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static bool s_active;
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bool Scheduler::is_active()
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{
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return s_active;
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}
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Thread::JoinBlocker::JoinBlocker(Thread& joinee, void*& joinee_exit_value)
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: m_joinee(joinee)
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, m_joinee_exit_value(joinee_exit_value)
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{
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ASSERT(m_joinee.m_joiner == nullptr);
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m_joinee.m_joiner = current;
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current->m_joinee = &joinee;
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}
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bool Thread::JoinBlocker::should_unblock(Thread& joiner, time_t, long)
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{
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return !joiner.m_joinee;
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}
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Thread::FileDescriptionBlocker::FileDescriptionBlocker(const FileDescription& description)
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: m_blocked_description(description)
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{
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}
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const FileDescription& Thread::FileDescriptionBlocker::blocked_description() const
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{
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return m_blocked_description;
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}
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Thread::AcceptBlocker::AcceptBlocker(const FileDescription& description)
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: FileDescriptionBlocker(description)
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{
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}
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bool Thread::AcceptBlocker::should_unblock(Thread&, time_t, long)
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{
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auto& socket = *blocked_description().socket();
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return socket.can_accept();
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}
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Thread::ReceiveBlocker::ReceiveBlocker(const FileDescription& description)
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: FileDescriptionBlocker(description)
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{
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}
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bool Thread::ReceiveBlocker::should_unblock(Thread&, time_t now_sec, long now_usec)
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{
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auto& socket = *blocked_description().socket();
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// FIXME: Block until the amount of data wanted is available.
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bool timed_out = now_sec > socket.receive_deadline().tv_sec || (now_sec == socket.receive_deadline().tv_sec && now_usec >= socket.receive_deadline().tv_usec);
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if (timed_out || blocked_description().can_read())
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return true;
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return false;
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}
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Thread::ConnectBlocker::ConnectBlocker(const FileDescription& description)
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: FileDescriptionBlocker(description)
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{
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}
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bool Thread::ConnectBlocker::should_unblock(Thread&, time_t, long)
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{
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auto& socket = *blocked_description().socket();
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return socket.setup_state() == Socket::SetupState::Completed;
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}
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Thread::WriteBlocker::WriteBlocker(const FileDescription& description)
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: FileDescriptionBlocker(description)
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{
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}
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bool Thread::WriteBlocker::should_unblock(Thread&, time_t, long)
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{
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return blocked_description().can_write();
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}
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Thread::ReadBlocker::ReadBlocker(const FileDescription& description)
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: FileDescriptionBlocker(description)
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{
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}
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bool Thread::ReadBlocker::should_unblock(Thread&, time_t, long)
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{
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// FIXME: Block until the amount of data wanted is available.
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return blocked_description().can_read();
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}
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Thread::ConditionBlocker::ConditionBlocker(const char* state_string, Function<bool()>&& condition)
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: m_block_until_condition(move(condition))
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, m_state_string(state_string)
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{
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ASSERT(m_block_until_condition);
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}
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bool Thread::ConditionBlocker::should_unblock(Thread&, time_t, long)
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{
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return m_block_until_condition();
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}
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Thread::SleepBlocker::SleepBlocker(u64 wakeup_time)
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: m_wakeup_time(wakeup_time)
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{
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}
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bool Thread::SleepBlocker::should_unblock(Thread&, time_t, long)
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{
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return m_wakeup_time <= g_uptime;
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}
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Thread::SelectBlocker::SelectBlocker(const timeval& tv, bool select_has_timeout, const FDVector& read_fds, const FDVector& write_fds, const FDVector& except_fds)
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: m_select_timeout(tv)
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, m_select_has_timeout(select_has_timeout)
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, m_select_read_fds(read_fds)
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, m_select_write_fds(write_fds)
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, m_select_exceptional_fds(except_fds)
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{
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}
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bool Thread::SelectBlocker::should_unblock(Thread& thread, time_t now_sec, long now_usec)
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{
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if (m_select_has_timeout) {
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if (now_sec > m_select_timeout.tv_sec || (now_sec == m_select_timeout.tv_sec && now_usec >= m_select_timeout.tv_usec))
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return true;
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}
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auto& process = thread.process();
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for (int fd : m_select_read_fds) {
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if (process.m_fds[fd].description->can_read())
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return true;
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}
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for (int fd : m_select_write_fds) {
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if (process.m_fds[fd].description->can_write())
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return true;
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}
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return false;
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}
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Thread::WaitBlocker::WaitBlocker(int wait_options, pid_t& waitee_pid)
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: m_wait_options(wait_options)
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, m_waitee_pid(waitee_pid)
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{
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}
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bool Thread::WaitBlocker::should_unblock(Thread& thread, time_t, long)
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{
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bool should_unblock = false;
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if (m_waitee_pid != -1) {
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auto* peer = Process::from_pid(m_waitee_pid);
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if (!peer)
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return true;
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}
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thread.process().for_each_child([&](Process& child) {
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if (m_waitee_pid != -1 && m_waitee_pid != child.pid())
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return IterationDecision::Continue;
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bool child_exited = child.is_dead();
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bool child_stopped = child.thread_count() && child.any_thread().state() == Thread::State::Stopped;
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bool wait_finished = ((m_wait_options & WEXITED) && child_exited)
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|| ((m_wait_options & WSTOPPED) && child_stopped);
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if (!wait_finished)
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return IterationDecision::Continue;
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m_waitee_pid = child.pid();
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should_unblock = true;
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return IterationDecision::Break;
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});
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return should_unblock;
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}
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Thread::SemiPermanentBlocker::SemiPermanentBlocker(Reason reason)
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: m_reason(reason)
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{
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}
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bool Thread::SemiPermanentBlocker::should_unblock(Thread&, time_t, long)
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{
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// someone else has to unblock us
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return false;
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}
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// Called by the scheduler on threads that are blocked for some reason.
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// Make a decision as to whether to unblock them or not.
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void Thread::consider_unblock(time_t now_sec, long now_usec)
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{
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switch (state()) {
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case Thread::Invalid:
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case Thread::Runnable:
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case Thread::Running:
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case Thread::Dead:
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case Thread::Stopped:
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case Thread::Queued:
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case Thread::Dying:
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/* don't know, don't care */
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return;
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case Thread::Blocked:
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ASSERT(m_blocker != nullptr);
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if (m_blocker->should_unblock(*this, now_sec, now_usec))
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unblock();
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return;
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case Thread::Skip1SchedulerPass:
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set_state(Thread::Skip0SchedulerPasses);
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return;
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case Thread::Skip0SchedulerPasses:
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set_state(Thread::Runnable);
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return;
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}
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}
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bool Scheduler::pick_next()
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{
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ASSERT_INTERRUPTS_DISABLED();
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ASSERT(!s_active);
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TemporaryChange<bool> change(s_active, true);
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ASSERT(s_active);
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if (!current) {
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// XXX: The first ever context_switch() goes to the idle process.
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// This to setup a reliable place we can return to.
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return context_switch(*g_colonel);
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}
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struct timeval now;
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kgettimeofday(now);
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auto now_sec = now.tv_sec;
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auto now_usec = now.tv_usec;
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// Check and unblock threads whose wait conditions have been met.
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Scheduler::for_each_nonrunnable([&](Thread& thread) {
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thread.consider_unblock(now_sec, now_usec);
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return IterationDecision::Continue;
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});
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Process::for_each([&](Process& process) {
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if (process.is_dead()) {
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if (current->pid() != process.pid() && (!process.ppid() || !Process::from_pid(process.ppid()))) {
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auto name = process.name();
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auto pid = process.pid();
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auto exit_status = Process::reap(process);
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dbgprintf("reaped unparented process %s(%u), exit status: %u\n", name.characters(), pid, exit_status);
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}
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return IterationDecision::Continue;
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}
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if (process.m_alarm_deadline && g_uptime > process.m_alarm_deadline) {
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process.m_alarm_deadline = 0;
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process.send_signal(SIGALRM, nullptr);
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}
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return IterationDecision::Continue;
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});
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// Dispatch any pending signals.
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// FIXME: Do we really need this to be a separate pass over the process list?
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Thread::for_each_living([](Thread& thread) -> IterationDecision {
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if (!thread.has_unmasked_pending_signals())
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return IterationDecision::Continue;
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// FIXME: It would be nice if the Scheduler didn't have to worry about who is "current"
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// For now, avoid dispatching signals to "current" and do it in a scheduling pass
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// while some other process is interrupted. Otherwise a mess will be made.
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if (&thread == current)
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return IterationDecision::Continue;
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// We know how to interrupt blocked processes, but if they are just executing
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// at some random point in the kernel, let them continue. They'll be in userspace
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// sooner or later and we can deliver the signal then.
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// FIXME: Maybe we could check when returning from a syscall if there's a pending
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// signal and dispatch it then and there? Would that be doable without the
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// syscall effectively being "interrupted" despite having completed?
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if (thread.in_kernel() && !thread.is_blocked() && !thread.is_stopped())
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return IterationDecision::Continue;
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// NOTE: dispatch_one_pending_signal() may unblock the process.
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bool was_blocked = thread.is_blocked();
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if (thread.dispatch_one_pending_signal() == ShouldUnblockThread::No)
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return IterationDecision::Continue;
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if (was_blocked) {
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dbgprintf("Unblock %s(%u) due to signal\n", thread.process().name().characters(), thread.pid());
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ASSERT(thread.m_blocker != nullptr);
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thread.m_blocker->set_interrupted_by_signal();
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thread.unblock();
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}
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return IterationDecision::Continue;
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});
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#ifdef SCHEDULER_RUNNABLE_DEBUG
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dbgprintf("Non-runnables:\n");
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Scheduler::for_each_nonrunnable([](Thread& thread) -> IterationDecision {
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auto& process = thread.process();
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dbgprintf("[K%x] %-12s %s(%u:%u) @ %w:%x\n", &process, thread.state_string(), process.name().characters(), process.pid(), thread.tid(), thread.tss().cs, thread.tss().eip);
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return IterationDecision::Continue;
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});
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for (u8 priority = (u8)ThreadPriority::Last; priority >= (u8)ThreadPriority::First; --priority) {
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dbgprintf("Runnables (%s):\n", to_string((ThreadPriority)priority));
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for_each_runnable_with_priority((ThreadPriority)priority, [](Thread& thread) -> IterationDecision {
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auto& process = thread.process();
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dbgprintf("[K%x] %-12s %s(%u:%u) @ %w:%x\n", &process, thread.state_string(), process.name().characters(), process.pid(), thread.tid(), thread.tss().cs, thread.tss().eip);
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return IterationDecision::Continue;
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});
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}
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#endif
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for (u8 priority = (u8)ThreadPriority::Last; priority >= (u8)ThreadPriority::First; --priority) {
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auto& runnable_list = g_scheduler_data->m_runnable_threads[priority - (u8)ThreadPriority::First];
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if (runnable_list.is_empty())
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continue;
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auto* previous_head = runnable_list.first();
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for (;;) {
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// Move head to tail.
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runnable_list.append(*runnable_list.first());
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auto* thread = runnable_list.first();
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if (!thread->process().is_being_inspected() && (thread->state() == Thread::Runnable || thread->state() == Thread::Running)) {
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#ifdef SCHEDULER_DEBUG
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dbgprintf("switch to %s(%u:%u) @ %w:%x\n", thread->process().name().characters(), thread->process().pid(), thread->tid(), thread->tss().cs, thread->tss().eip);
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#endif
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return context_switch(*thread);
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}
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if (thread == previous_head)
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break;
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}
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}
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// Nothing wants to run. Send in the colonel!
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return context_switch(*g_colonel);
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}
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bool Scheduler::donate_to(Thread* beneficiary, const char* reason)
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{
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InterruptDisabler disabler;
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if (!Thread::is_thread(beneficiary))
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return false;
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(void)reason;
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unsigned ticks_left = current->ticks_left();
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if (!beneficiary || beneficiary->state() != Thread::Runnable || ticks_left <= 1)
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return yield();
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unsigned ticks_to_donate = min(ticks_left - 1, time_slice_for(beneficiary->priority()));
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#ifdef SCHEDULER_DEBUG
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dbgprintf("%s(%u:%u) donating %u ticks to %s(%u:%u), reason=%s\n", current->process().name().characters(), current->pid(), current->tid(), ticks_to_donate, beneficiary->process().name().characters(), beneficiary->pid(), beneficiary->tid(), reason);
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#endif
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context_switch(*beneficiary);
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beneficiary->set_ticks_left(ticks_to_donate);
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switch_now();
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return false;
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}
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bool Scheduler::yield()
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{
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InterruptDisabler disabler;
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ASSERT(current);
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// dbgprintf("%s(%u:%u) yield()\n", current->process().name().characters(), current->pid(), current->tid());
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if (!pick_next())
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return false;
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// dbgprintf("yield() jumping to new process: sel=%x, %s(%u:%u)\n", current->far_ptr().selector, current->process().name().characters(), current->pid(), current->tid());
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switch_now();
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return true;
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}
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void Scheduler::pick_next_and_switch_now()
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{
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bool someone_wants_to_run = pick_next();
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ASSERT(someone_wants_to_run);
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switch_now();
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}
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void Scheduler::switch_now()
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{
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Descriptor& descriptor = get_gdt_entry(current->selector());
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descriptor.type = 9;
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flush_gdt();
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asm("sti\n"
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"ljmp *(%%eax)\n" ::"a"(¤t->far_ptr()));
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}
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bool Scheduler::context_switch(Thread& thread)
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{
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thread.set_ticks_left(time_slice_for(thread.priority()));
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thread.did_schedule();
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if (current == &thread)
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return false;
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if (current) {
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// If the last process hasn't blocked (still marked as running),
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// mark it as runnable for the next round.
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if (current->state() == Thread::Running)
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current->set_state(Thread::Runnable);
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#ifdef LOG_EVERY_CONTEXT_SWITCH
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dbgprintf("Scheduler: %s(%u:%u) -> %s(%u:%u) [%s] %w:%x\n",
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current->process().name().characters(), current->process().pid(), current->tid(),
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thread.process().name().characters(), thread.process().pid(), thread.tid(),
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to_string(thread.priority()),
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thread.tss().cs, thread.tss().eip);
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#endif
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}
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current = &thread;
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thread.set_state(Thread::Running);
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if (!thread.selector()) {
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thread.set_selector(gdt_alloc_entry());
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auto& descriptor = get_gdt_entry(thread.selector());
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descriptor.set_base(&thread.tss());
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descriptor.set_limit(0xffff);
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descriptor.dpl = 0;
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descriptor.segment_present = 1;
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descriptor.granularity = 1;
|
|
descriptor.zero = 0;
|
|
descriptor.operation_size = 1;
|
|
descriptor.descriptor_type = 0;
|
|
}
|
|
|
|
if (!thread.thread_specific_data().is_null()) {
|
|
auto& descriptor = thread_specific_descriptor();
|
|
descriptor.set_base(thread.thread_specific_data().as_ptr());
|
|
descriptor.set_limit(sizeof(ThreadSpecificData*));
|
|
}
|
|
|
|
auto& descriptor = get_gdt_entry(thread.selector());
|
|
descriptor.type = 11; // Busy TSS
|
|
flush_gdt();
|
|
return true;
|
|
}
|
|
|
|
static void initialize_redirection()
|
|
{
|
|
auto& descriptor = get_gdt_entry(s_redirection.selector);
|
|
descriptor.set_base(&s_redirection.tss);
|
|
descriptor.set_limit(0xffff);
|
|
descriptor.dpl = 0;
|
|
descriptor.segment_present = 1;
|
|
descriptor.granularity = 1;
|
|
descriptor.zero = 0;
|
|
descriptor.operation_size = 1;
|
|
descriptor.descriptor_type = 0;
|
|
descriptor.type = 9;
|
|
flush_gdt();
|
|
}
|
|
|
|
void Scheduler::prepare_for_iret_to_new_process()
|
|
{
|
|
auto& descriptor = get_gdt_entry(s_redirection.selector);
|
|
descriptor.type = 9;
|
|
s_redirection.tss.backlink = current->selector();
|
|
load_task_register(s_redirection.selector);
|
|
}
|
|
|
|
void Scheduler::prepare_to_modify_tss(Thread& thread)
|
|
{
|
|
// This ensures that a currently running process modifying its own TSS
|
|
// in order to yield() and end up somewhere else doesn't just end up
|
|
// right after the yield().
|
|
if (current == &thread)
|
|
load_task_register(s_redirection.selector);
|
|
}
|
|
|
|
Process* Scheduler::colonel()
|
|
{
|
|
return s_colonel_process;
|
|
}
|
|
|
|
void Scheduler::initialize()
|
|
{
|
|
g_scheduler_data = new SchedulerData;
|
|
g_finalizer_wait_queue = new WaitQueue;
|
|
s_redirection.selector = gdt_alloc_entry();
|
|
initialize_redirection();
|
|
s_colonel_process = Process::create_kernel_process(g_colonel, "colonel", nullptr);
|
|
// Make sure the colonel uses a smallish time slice.
|
|
g_colonel->set_priority(ThreadPriority::Idle);
|
|
load_task_register(s_redirection.selector);
|
|
}
|
|
|
|
void Scheduler::timer_tick(RegisterDump& regs)
|
|
{
|
|
if (!current)
|
|
return;
|
|
|
|
++g_uptime;
|
|
|
|
timeval tv;
|
|
tv.tv_sec = RTC::boot_time() + PIT::seconds_since_boot();
|
|
tv.tv_usec = PIT::ticks_this_second() * 1000;
|
|
Process::update_info_page_timestamp(tv);
|
|
|
|
if (current->process().is_profiling()) {
|
|
auto backtrace = current->raw_backtrace(regs.ebp);
|
|
auto& sample = Profiling::next_sample_slot();
|
|
sample.pid = current->pid();
|
|
sample.tid = current->tid();
|
|
sample.timestamp = g_uptime;
|
|
for (size_t i = 0; i < min((size_t)backtrace.size(), Profiling::max_stack_frame_count); ++i) {
|
|
sample.frames[i] = backtrace[i];
|
|
}
|
|
}
|
|
|
|
if (current->tick())
|
|
return;
|
|
|
|
auto& outgoing_tss = current->tss();
|
|
|
|
if (!pick_next())
|
|
return;
|
|
|
|
outgoing_tss.gs = regs.gs;
|
|
outgoing_tss.fs = regs.fs;
|
|
outgoing_tss.es = regs.es;
|
|
outgoing_tss.ds = regs.ds;
|
|
outgoing_tss.edi = regs.edi;
|
|
outgoing_tss.esi = regs.esi;
|
|
outgoing_tss.ebp = regs.ebp;
|
|
outgoing_tss.ebx = regs.ebx;
|
|
outgoing_tss.edx = regs.edx;
|
|
outgoing_tss.ecx = regs.ecx;
|
|
outgoing_tss.eax = regs.eax;
|
|
outgoing_tss.eip = regs.eip;
|
|
outgoing_tss.cs = regs.cs;
|
|
outgoing_tss.eflags = regs.eflags;
|
|
|
|
// Compute process stack pointer.
|
|
// Add 16 for CS, EIP, EFLAGS, exception code (interrupt mechanic)
|
|
outgoing_tss.esp = regs.esp + 16;
|
|
outgoing_tss.ss = regs.ss;
|
|
|
|
if ((outgoing_tss.cs & 3) != 0) {
|
|
outgoing_tss.ss = regs.ss_if_crossRing;
|
|
outgoing_tss.esp = regs.esp_if_crossRing;
|
|
}
|
|
prepare_for_iret_to_new_process();
|
|
|
|
// Set the NT (nested task) flag.
|
|
asm(
|
|
"pushf\n"
|
|
"orl $0x00004000, (%esp)\n"
|
|
"popf\n");
|
|
}
|
|
|
|
static bool s_should_stop_idling = false;
|
|
|
|
void Scheduler::stop_idling()
|
|
{
|
|
if (current != g_colonel)
|
|
return;
|
|
|
|
s_should_stop_idling = true;
|
|
}
|
|
|
|
void Scheduler::idle_loop()
|
|
{
|
|
for (;;) {
|
|
asm("hlt");
|
|
if (s_should_stop_idling) {
|
|
s_should_stop_idling = false;
|
|
yield();
|
|
}
|
|
}
|
|
}
|