#include "threads/flags.h"
#include "threads/interrupt.h"
#include "threads/intr-stubs.h"
-#include "threads/mmu.h"
#include "threads/palloc.h"
#include "threads/switch.h"
#include "threads/synch.h"
+#include "threads/vaddr.h"
#ifdef USERPROG
#include "userprog/process.h"
#endif
void *aux; /* Auxiliary data for function. */
};
+/* Statistics. */
+static long long idle_ticks; /* # of timer ticks spent idle. */
+static long long kernel_ticks; /* # of timer ticks in kernel threads. */
+static long long user_ticks; /* # of timer ticks in user programs. */
+
+/* Scheduling. */
+#define TIME_SLICE 4 /* # of timer ticks to give each thread. */
+static unsigned thread_ticks; /* # of timer ticks since last yield. */
+
+/* If false (default), use round-robin scheduler.
+ If true, use multi-level feedback queue scheduler.
+ Controlled by kernel command-line options "-o mlfqs".
+ Note that the command line is not parsed until well after
+ thread_init() is called. */
+bool thread_mlfqs;
+
static void kernel_thread (thread_func *, void *aux);
static void idle (void *aux UNUSED);
static struct thread *running_thread (void);
static struct thread *next_thread_to_run (void);
static void init_thread (struct thread *, const char *name, int priority);
-static bool is_thread (struct thread *);
+static bool is_thread (struct thread *) UNUSED;
static void *alloc_frame (struct thread *, size_t size);
static void schedule (void);
void schedule_tail (struct thread *prev);
static tid_t allocate_tid (void);
/* Initializes the threading system by transforming the code
- that's currently running into a thread. Note that this is
- possible only because the loader was careful to put the bottom
- of the stack at a page boundary; it won't work in general.
- Also initializes the run queue.
+ that's currently running into a thread. This can't work in
+ general and it is possible in this case only because loader.S
+ was careful to put the bottom of the stack at a page boundary.
+
+ Also initializes the run queue and the tid lock.
After calling this function, be sure to initialize the page
allocator before trying to create any threads with
- thread_create(). */
+ thread_create().
+
+ The kernel command line is not parsed until *after* this
+ function returns, so that when this function runs,
+ thread_mlfqs is always false.
+
+ It is not safe to call thread_current() until this function
+ finishes. */
void
thread_init (void)
{
ASSERT (intr_get_level () == INTR_OFF);
- lock_init (&tid_lock, "tid");
+ lock_init (&tid_lock);
list_init (&ready_list);
/* Set up a thread structure for the running thread. */
}
/* Starts preemptive thread scheduling by enabling interrupts.
- Also creates the idle thread. */
+ Also creates the idle thread.
+
+ By the time this function runs, thread_mlfqs has been properly
+ initialized to its final value. */
void
thread_start (void)
{
- thread_create ("idle", PRI_DEFAULT, idle, NULL);
+ /* Create the idle thread. */
+ struct semaphore idle_started;
+ sema_init (&idle_started, 0);
+ thread_create ("idle", PRI_MIN, idle, &idle_started);
+
+ /* Start preemptive thread scheduling. */
intr_enable ();
+
+ /* Wait for the idle thread to initialize idle_thread. */
+ sema_down (&idle_started);
+}
+
+/* Called by the timer interrupt handler at each timer tick.
+ Thus, this function runs in an external interrupt context. */
+void
+thread_tick (void)
+{
+ struct thread *t = thread_current ();
+
+ /* Update statistics. */
+ if (t == idle_thread)
+ idle_ticks++;
+#ifdef USERPROG
+ else if (t->pagedir != NULL)
+ user_ticks++;
+#endif
+ else
+ kernel_ticks++;
+
+ /* Enforce preemption. */
+ if (++thread_ticks >= TIME_SLICE)
+ intr_yield_on_return ();
+}
+
+/* Prints thread statistics. */
+void
+thread_print_stats (void)
+{
+ printf ("Thread: %lld idle ticks, %lld kernel ticks, %lld user ticks\n",
+ idle_ticks, kernel_ticks, user_ticks);
}
/* Creates a new kernel thread named NAME with the given initial
PRIORITY, which executes FUNCTION passing AUX as the argument,
- and adds it to the ready queue. If thread_start() has been
- called, then the new thread may be scheduled before
- thread_create() returns. It could even exit before
- thread_create() returns. Use a semaphore or some other form
- of synchronization if you need to ensure ordering. Returns
- the thread identifier for the new thread, or TID_ERROR if
- creation fails.
+ and adds it to the ready queue. Returns the thread identifier
+ for the new thread, or TID_ERROR if creation fails.
+
+ If thread_start() has been called, then the new thread may be
+ scheduled before thread_create() returns. It could even exit
+ before thread_create() returns. Contrariwise, the original
+ thread may run for any amount of time before the new thread is
+ scheduled. Use a semaphore or some other form of
+ synchronization if you need to ensure ordering.
The code provided sets the new thread's `priority' member to
PRIORITY, but no actual priority scheduling is implemented.
return tid;
}
-/* Transitions a blocked thread T from its current state to the
- ready-to-run state. This is an error if T is not blocked.
- (Use thread_yield() to make the running thread ready.) */
+/* Puts the current thread to sleep. It will not be scheduled
+ again until awoken by thread_unblock().
+
+ This function must be called with interrupts turned off. It
+ is usually a better idea to use one of the synchronization
+ primitives in synch.h. */
+void
+thread_block (void)
+{
+ ASSERT (!intr_context ());
+ ASSERT (intr_get_level () == INTR_OFF);
+
+ thread_current ()->status = THREAD_BLOCKED;
+ schedule ();
+}
+
+/* Transitions a blocked thread T to the ready-to-run state.
+ This is an error if T is not blocked. (Use thread_yield() to
+ make the running thread ready.) */
void
thread_unblock (struct thread *t)
{
ASSERT (!intr_context ());
old_level = intr_disable ();
- list_push_back (&ready_list, &cur->elem);
+ if (cur != idle_thread)
+ list_push_back (&ready_list, &cur->elem);
cur->status = THREAD_READY;
schedule ();
intr_set_level (old_level);
}
-/* Puts the current thread to sleep. It will not be scheduled
- again until awoken by thread_unblock().
+/* Sets the current thread's priority to NEW_PRIORITY. */
+void
+thread_set_priority (int new_priority)
+{
+ thread_current ()->priority = new_priority;
+}
- This function must be called with interrupts turned off. It
- is usually a better idea to use one of the synchronization
- primitives in synch.h. */
+/* Returns the current thread's priority. */
+int
+thread_get_priority (void)
+{
+ return thread_current ()->priority;
+}
+
+/* Sets the current thread's nice value to NICE. */
void
-thread_block (void)
+thread_set_nice (int nice UNUSED)
{
- ASSERT (!intr_context ());
- ASSERT (intr_get_level () == INTR_OFF);
+ /* Not yet implemented. */
+}
- thread_current ()->status = THREAD_BLOCKED;
- schedule ();
+/* Returns the current thread's nice value. */
+int
+thread_get_nice (void)
+{
+ /* Not yet implemented. */
+ return 0;
+}
+
+/* Returns 100 times the system load average. */
+int
+thread_get_load_avg (void)
+{
+ /* Not yet implemented. */
+ return 0;
+}
+
+/* Returns 100 times the current thread's recent_cpu value. */
+int
+thread_get_recent_cpu (void)
+{
+ /* Not yet implemented. */
+ return 0;
}
\f
-/* Idle thread. Executes when no other thread is ready to run. */
+/* Idle thread. Executes when no other thread is ready to run.
+
+ The idle thread is initially put on the ready list by
+ thread_start(). It will be scheduled once initially, at which
+ point it initializes idle_thread, "up"s the semaphore passed
+ to it to enable thread_start() to continue, and immediately
+ blocks. After that, the idle thread never appears in the
+ ready list. It is returned by next_thread_to_run() as a
+ special case when the ready list is empty. */
static void
-idle (void *aux UNUSED)
+idle (void *idle_started_ UNUSED)
{
+ struct semaphore *idle_started = idle_started_;
idle_thread = thread_current ();
+ sema_up (idle_started);
for (;;)
{
/* Let someone else run. */
intr_disable ();
thread_block ();
- intr_enable ();
- /* Use CPU `hlt' instruction to wait for interrupt. */
- asm ("hlt");
+ /* Re-enable interrupts and wait for the next one.
+
+ The `sti' instruction disables interrupts until the
+ completion of the next instruction, so these two
+ instructions are executed atomically. This atomicity is
+ important; otherwise, an interrupt could be handled
+ between re-enabling interrupts and waiting for the next
+ one to occur, wasting as much as one clock tick worth of
+ time.
+
+ See [IA32-v2a] "HLT", [IA32-v2b] "STI", and [IA32-v3a]
+ 7.11.1 "HLT Instruction". */
+ asm volatile ("sti; hlt" : : : "memory");
}
}
down to the start of a page. Because `struct thread' is
always at the beginning of a page and the stack pointer is
somewhere in the middle, this locates the curent thread. */
- asm ("movl %%esp, %0\n" : "=g" (esp));
+ asm ("mov %%esp, %0" : "=g" (esp));
return pg_round_down (esp);
}
/* Returns true if T appears to point to a valid thread. */
static bool
-is_thread (struct thread *t)
+is_thread (struct thread *t)
{
return t != NULL && t->magic == THREAD_MAGIC;
}
the first time a thread is scheduled it is called by
switch_entry() (see switch.S).
+ It's not safe to call printf() until the thread switch is
+ complete. In practice that means that printf()s should be
+ added at the end of the function.
+
After this function and its caller returns, the thread switch
is complete. */
void
/* Mark us as running. */
cur->status = THREAD_RUNNING;
+ /* Start new time slice. */
+ thread_ticks = 0;
+
#ifdef USERPROG
/* Activate the new address space. */
process_activate ();
/* If the thread we switched from is dying, destroy its struct
thread. This must happen late so that thread_exit() doesn't
- pull out the rug under itself. */
- if (prev != NULL && prev->status == THREAD_DYING)
+ pull out the rug under itself. (We don't free
+ initial_thread because its memory was not obtained via
+ palloc().) */
+ if (prev != NULL && prev->status == THREAD_DYING && prev != initial_thread)
{
ASSERT (prev != cur);
- if (prev != initial_thread)
- palloc_free_page (prev);
+ palloc_free_page (prev);
}
}
/* Schedules a new process. At entry, interrupts must be off and
the running process's state must have been changed from
running to some other state. This function finds another
- thread to run and switches to it. */
+ thread to run and switches to it.
+
+ It's not safe to call printf() until schedule_tail() has
+ completed. */
static void
schedule (void)
{
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