From 044c383a0f8ed99db174ad85744006a741792cd7 Mon Sep 17 00:00:00 2001
From: Gleb Koval <gleb@koval.net>
Date: Thu, 17 Oct 2024 02:38:57 +0100
Subject: [PATCH] fix mlfqs tests, complete BSD scheduling

---
 src/devices/timer.c  |  5 -----
 src/threads/synch.c  |  1 +
 src/threads/thread.c | 37 +++++++++++++++++++++++++++++++++----
 3 files changed, 34 insertions(+), 9 deletions(-)

diff --git a/src/devices/timer.c b/src/devices/timer.c
index 3e481cc..4bb602e 100644
--- a/src/devices/timer.c
+++ b/src/devices/timer.c
@@ -199,10 +199,6 @@ static void
 timer_interrupt (struct intr_frame *args UNUSED)
 {
   ticks++;
-  if (ticks % TIMER_FREQ == 0)
-  {
-    calculate_recent_cpu ();
-  }
   for (struct list_elem *e = list_begin (&sleeping_threads);
        e != list_end (&sleeping_threads); e = list_next (e))
     {
@@ -212,7 +208,6 @@ timer_interrupt (struct intr_frame *args UNUSED)
       else
         break;
     }
-  thread_increment_recent_cpu ();
   thread_tick ();
 }
 
diff --git a/src/threads/synch.c b/src/threads/synch.c
index 7776cb0..9a55247 100644
--- a/src/threads/synch.c
+++ b/src/threads/synch.c
@@ -233,6 +233,7 @@ lock_release (struct lock *lock)
 
   lock->holder = NULL;
   sema_up (&lock->semaphore);
+  thread_yield ();
 }
 
 /* Returns true if the current thread holds LOCK, false
diff --git a/src/threads/thread.c b/src/threads/thread.c
index 6657d9f..8ef0469 100644
--- a/src/threads/thread.c
+++ b/src/threads/thread.c
@@ -73,6 +73,8 @@ 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 bool thread_priority_less (const struct list_elem *a,
+                                  const struct list_elem *b, void *aux UNUSED);
 static void schedule (void);
 void thread_schedule_tail (struct thread *prev);
 static tid_t allocate_tid (void);
@@ -157,8 +159,11 @@ thread_tick (void)
   int64_t ticks = timer_ticks ();
   if (thread_mlfqs && (ticks % TIMER_FREQ == 0))
     {
+      size_t ready = threads_ready ();
+      if (t != idle_thread)
+        ready++;
       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);
+      fp32_t new_coeff = fp_div_int (int_to_fp (ready), 60);
       load_avg = fp_add (old_coeff, new_coeff);
 
       thread_foreach (thread_update_recent_cpu, NULL);
@@ -284,7 +289,10 @@ thread_unblock (struct thread *t)
 
   old_level = intr_disable ();
   ASSERT (t->status == THREAD_BLOCKED);
-  list_push_back (&ready_list, &t->elem);
+  if (thread_mlfqs)
+    list_insert_ordered (&ready_list, &t->elem, thread_priority_less, NULL);
+  else
+    list_push_back (&ready_list, &t->elem);
   t->status = THREAD_READY;
   intr_set_level (old_level);
 }
@@ -354,8 +362,14 @@ thread_yield (void)
   ASSERT (!intr_context ());
 
   old_level = intr_disable ();
-  if (cur != idle_thread) 
-    list_push_back (&ready_list, &cur->elem);
+  if (cur != idle_thread)
+    {
+      if (thread_mlfqs)
+        list_insert_ordered (&ready_list, &cur->elem, thread_priority_less,
+                             NULL);
+      else
+        list_push_back (&ready_list, &cur->elem);
+    }
   cur->status = THREAD_READY;
   schedule ();
   intr_set_level (old_level);
@@ -417,6 +431,10 @@ thread_set_nice (int nice)
   struct thread *t = thread_current ();
   t->nice = nice;
   int priority = calculate_bsd_priority (t->recent_cpu, t->nice);
+  struct thread *next_t
+      = list_entry (list_begin (&ready_list), struct thread, elem);
+  if (priority < next_t->priority)
+    thread_yield ();
 }
 
 /* Returns the current thread's nice value. */
@@ -622,6 +640,17 @@ calculate_bsd_priority (fp32_t recent_cpu, int nice)
   return priority;
 }
 
+/* Returns true if thread a's priority is strictly greater than
+   thread b's priority. */
+static bool
+thread_priority_less (const struct list_elem *a, const struct list_elem *b,
+                      void *aux UNUSED)
+{
+  struct thread *ta = list_entry (a, struct thread, elem);
+  struct thread *tb = list_entry (b, struct thread, elem);
+  return ta->priority > tb->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.