X-Git-Url: https://pintos-os.org/cgi-bin/gitweb.cgi?p=pintos-anon;a=blobdiff_plain;f=src%2Fthreads%2Fthread.c;h=1dc34adac7770f6bc53b5e5a1fb6b533ec0043f4;hp=01ce7d33227a19196762199f3c349bab4890b688;hb=49c19e58aa14fba779bfe331b1ebaba62d31dfa5;hpb=7d4e3dda080a47db88616f1c0d975f2091be47f1

diff --git a/src/threads/thread.c b/src/threads/thread.c
index 01ce7d3..1dc34ad 100644
--- a/src/threads/thread.c
+++ b/src/threads/thread.c
@@ -7,10 +7,10 @@
 #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
@@ -46,13 +46,24 @@ 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);
@@ -67,13 +78,20 @@ static tid_t allocate_tid (void);
 
    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. */
@@ -84,20 +102,33 @@ thread_init (void)
 }
 
 /* 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 to
-   update statistics. */
+/* 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
@@ -106,6 +137,10 @@ thread_tick (void)
 #endif
   else
     kernel_ticks++;
+
+  /* Enforce preemption. */
+  if (++thread_ticks >= TIME_SLICE)
+    intr_yield_on_return ();
 }
 
 /* Prints thread statistics. */
@@ -118,13 +153,15 @@ thread_print_stats (void)
 
 /* 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.
@@ -266,28 +303,93 @@ thread_yield (void)
   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);
 }
+
+/* Sets the current thread's priority to NEW_PRIORITY. */
+void
+thread_set_priority (int new_priority) 
+{
+  thread_current ()->priority = new_priority;
+}
+
+/* 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_set_nice (int nice UNUSED) 
+{
+  /* Not yet implemented. */
+}
+
+/* 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;
+}
 
-/* 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.
-         See [IA32-v2a] "HLT" and [IA32-v3] 7.7. */
-      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");
     }
 }
 
@@ -312,13 +414,13 @@ running_thread (void)
      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 ("mov %0, %%esp" : "=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;
 }
@@ -393,6 +495,9 @@ schedule_tail (struct thread *prev)
   /* Mark us as running. */
   cur->status = THREAD_RUNNING;
 
+  /* Start new time slice. */
+  thread_ticks = 0;
+
 #ifdef USERPROG
   /* Activate the new address space. */
   process_activate ();
@@ -400,12 +505,13 @@ schedule_tail (struct thread *prev)
 
   /* 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);
     }
 }