Implement BSD calculations

- load_avg, recent_cpu, priority calculations
- reduce frac bits to 14

src/threads/fixed-point.h

@@ -8,7 +8,7 @@ typedef struct
 } fp32_t;
 
 /* Fixed Point Arithmetic bit count constants */
-#define NUM_FRAC_BITS 20
+#define NUM_FRAC_BITS 14
 #define NUM_INT_BITS (31 - NUM_FRAC_BITS)
 #define CONVERSION_CONST (1 << NUM_FRAC_BITS) /* f = 2^q, (2^20) */
 

src/threads/thread.c

@@ -4,6 +4,7 @@
 #include <random.h>
 #include <stdio.h>
 #include <string.h>
+#include "devices/timer.h"
 #include "threads/fixed-point.h"
 #include "threads/flags.h"
 #include "threads/interrupt.h"
@@ -50,6 +51,7 @@ struct kernel_thread_frame
 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. */
+static fp32_t load_avg = { 0 }; /* System load average. */
 
 /* Scheduling. */
 #define TIME_SLICE 4            /* # of timer ticks to give each thread. */
@@ -65,9 +67,12 @@ 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, fp32_t recent_cpu);
+static void init_thread (struct thread *, const char *name, int nice,
+                         int priority, fp32_t recent_cpu);
 static bool is_thread (struct thread *) UNUSED;
 static void *alloc_frame (struct thread *, size_t size);
+static int calculate_bsd_priority (fp32_t recent_cpu, int nice);
+static void thread_update_recent_cpu (struct thread *t, void *aux UNUSED);
 static void schedule (void);
 void thread_schedule_tail (struct thread *prev);
 static tid_t allocate_tid (void);
@@ -97,7 +102,8 @@ thread_init (void)
   /* Set up a thread structure for the running thread. */
   initial_thread = running_thread ();
   fp32_t initial_thread_recent_cpu = { 0 };
-  init_thread (initial_thread, "main", PRI_DEFAULT, initial_thread_recent_cpu);
+  init_thread (initial_thread, "main", NICE_DEFAULT, PRI_DEFAULT,
+               initial_thread_recent_cpu);
   initial_thread->status = THREAD_RUNNING;
   initial_thread->tid = allocate_tid ();
 }
@@ -147,6 +153,25 @@ thread_tick (void)
   else
     kernel_ticks++;
 
+  /* Update system load_avg and all threads recent_cpu every second. */
+  int64_t ticks = timer_ticks ();
+  if (ticks % TIMER_FREQ == 0)
+    {
+      fp32_t old_coeff = fp_mul (fp_div_int (int_to_fp (59), 60), load_avg);
+      fp32_t new_coeff = fp_div_int (int_to_fp (threads_ready ()), 60);
+      load_avg = fp_add (old_coeff, new_coeff);
+
+      thread_foreach (thread_update_recent_cpu, NULL);
+    }
+
+  /* Update current thread's recent_cpu. */
+  if (t != idle_thread)
+    {
+      t->recent_cpu = fp_add_int (t->recent_cpu, 1);
+      if (ticks % 4 == 0) // recent_cpu was updated, update priority.
+        t->priority = calculate_bsd_priority (t->recent_cpu, t->nice);
+    }
+
   /* Enforce preemption. */
   if (++thread_ticks >= TIME_SLICE)
     intr_yield_on_return ();
@@ -194,8 +219,8 @@ thread_create (const char *name, int priority,
     return TID_ERROR;
 
   /* Initialize thread. */
-  fp32_t parent_recent_cpu = thread_current ()->recent_cpu;
-  init_thread (t, name, priority, parent_recent_cpu);
+  struct thread *pt = thread_current ();
+  init_thread (t, name, pt->nice, priority, pt->recent_cpu);
   tid = t->tid = allocate_tid ();
 
   /* Prepare thread for first run by initializing its stack.
@@ -367,44 +392,29 @@ thread_get_priority (void)
   return thread_current ()->priority;
 }
 
-/* Calculates priority for the current thread */
-int
-calculate_priority (void)
+/* Updates recent_cpu for a thread. */
+static void
+thread_update_recent_cpu (struct thread *t, void *aux UNUSED)
 {
-	/* Not yet implemented */
-	return 0;
-}
-
-void
-calculate_recent_cpu (void)
-{
-  struct thread *t = thread_current ();
   fp32_t curr_recent_cpu = t->recent_cpu;
-  fp32_t curr_load_avg = fp_mul_int(thread_get_load_avg (), 2);
-  fp32_t recent_cpu_coeff = fp_div(curr_load_avg, fp_add_int(curr_load_avg, 1));
-  fp32_t new_recent_cpu = fp_add_int(fp_mul(recent_cpu_coeff, curr_recent_cpu), thread_get_nice ());
-  t->recent_cpu = new_recent_cpu;
-}
-
-void
-thread_increment_recent_cpu (void)
-{
-  struct thread *t = thread_current ();
-  if (t == idle_thread)
-  {
-    return;
-  }
-  fp32_t old_recent_cpu = t->recent_cpu;
-  old_recent_cpu.raw = old_recent_cpu.raw + 1;
-  t->recent_cpu = old_recent_cpu;
+  fp32_t dbl_load_avg = fp_mul_int (load_avg, 2);
+  fp32_t recent_cpu_coeff
+      = fp_div (dbl_load_avg, fp_add_int (dbl_load_avg, 1));
+  t->recent_cpu
+      = fp_add_int (fp_mul (recent_cpu_coeff, curr_recent_cpu), t->nice);
+  // recent_cpu was updated, update priority.
+  t->priority = calculate_bsd_priority (t->recent_cpu, t->nice);
 }
 
 /* Sets the current thread's nice value to NICE. */
 void
 thread_set_nice (int nice)
 {
-  thread_current ()->nice = nice;
-  calculate_priority ();
+  ASSERT (NICE_MIN <= nice && nice <= NICE_MAX);
+
+  struct thread *t = thread_current ();
+  t->nice = nice;
+  int priority = calculate_bsd_priority (t->recent_cpu, t->nice);
 }
 
 /* Returns the current thread's nice value. */
@@ -418,8 +428,7 @@ thread_get_nice (void)
 int
 thread_get_load_avg (void) 
 {
-  /* Not yet implemented. */
-  return 0;
+  return fp_round (fp_mul_int (load_avg, 100));
 }
 
 /* Returns 100 times the current thread's recent_cpu value. */
@@ -502,7 +511,8 @@ is_thread (struct thread *t)
 /* Does basic initialization of T as a blocked thread named
    NAME. */
 static void
-init_thread (struct thread *t, const char *name, int priority, fp32_t recent_cpu)
+init_thread (struct thread *t, const char *name, int nice, int priority,
+             fp32_t recent_cpu)
 {
   enum intr_level old_level;
 
@@ -514,9 +524,11 @@ init_thread (struct thread *t, const char *name, int priority, fp32_t recent_cpu
   t->status = THREAD_BLOCKED;
   strlcpy (t->name, name, sizeof t->name);
   t->stack = (uint8_t *) t + PGSIZE;
-  t->priority = priority;
-  t->magic = THREAD_MAGIC;
+  t->priority
+      = thread_mlfqs ? calculate_bsd_priority (recent_cpu, nice) : priority;
+  t->nice = nice;
   t->recent_cpu = recent_cpu;
+  t->magic = THREAD_MAGIC;
 
   old_level = intr_disable ();
   list_push_back (&all_list, &t->allelem);
@@ -596,8 +608,19 @@ thread_schedule_tail (struct thread *prev)
     }
 }
 
-/* Schedules a new process.  At entry, interrupts must be off and
-   the running process's state must have been changed from
+/* Calculates BSD priority for a thread */
+static int
+calculate_bsd_priority (fp32_t recent_cpu, int nice)
+{
+  int priority = PRI_MAX - (fp_round (recent_cpu) / 4) - (nice * 2);
+  if (priority < PRI_MIN)
+    return PRI_MIN;
+  if (priority > PRI_MAX)
+    return PRI_MAX;
+  return priority;
+}
+
+/* ss's state must have been changed from
    running to some other state.  This function finds another
    thread to run and switches to it.
 

src/threads/thread.h

@@ -25,6 +25,10 @@ typedef int tid_t;
 #define PRI_DEFAULT 31                  /* Default priority. */
 #define PRI_MAX 63                      /* Highest priority. */
 
+#define NICE_MIN -20   /* Lowest niceness. */
+#define NICE_DEFAULT 0 /* Default niceness. */
+#define NICE_MAX 20    /* Highest niceness. */
+
 /* A kernel thread or user process.
 
    Each thread structure is stored in its own 4 kB page.  The