section notes 2/22/2007


PROJECT 2B

Discuss grading guidelines


preemption:
(Graded on 0-15 scale)
	-8 non-compilation
	-5 not turning on the timer in the first place
	-3 splx(LOW) before sthread_switch()
	-3 disabling interrupts in user_yield before switch
	-3 not using proper stack-like behavior of splx()
	-3 start function needs splx(LOW)
	-2 atomic_test_and_sets in places not required.
	-2 sthread_enqueue requires synchronization.
	-2 improper interaction between yield/join with splx()
	-2 mutex functions need splx() in some areas.
	-1 superfluous interrupt disable/enabling in same function
	-1 sthread_exit should not need extra splx(LOW)
	-1 (misc. bad style)

And for the burgers problem:
(Graded on 0-10 scale)
	-5 non-compilation
	-2 program segfaults
	-2 not implementing a stack.
	-2 use of shared mem without synchronization in producer
	-2 use of shared mem without synchronization in consumer
	-2 no condition variables to mediate access to stack (possible
starvation)
	-1 main() does not join children; instead looks at variables
		w/o synchronization to determine finish condition
	-1 main() only joins last child spawned instead of all children




Go over example of burger problem done correctly:

mutex stack_lock;
condition_var not_empty;

int burgers_to_make = N;
int next_burger = 0;
int num_consumed = 0;

int producer(void *arg)
{
  int my_id = (int) arg;
  while(true)
  {
    mutex_lock(stack_lock); 
    if(last_made == burgers_to_make)
      break;
    else
    {
      printf("Cook %i made burger %i\n", my_id, next_burger);
      stack_push(next_burger++);
      notify(not_empty);
    }

    mutex_unlock(stack_lock);
  }

  mutex_unlock(stack_lock);
  broadcast(not_empty);
  return 0;
}


int consumer(void *arg)
{
  int my_id = (int) arg;
  int burger;

  while(true)
  {
    mutex_lock(stack_lock); 

    if(num_consumed == burgers_to_make) 
	  break;

    while(stack_size() == 0)
	{
      if(num_consumed == burgers_to_make) 
	  {
	    mutex_unlock(stack_lock);
	    thread_exit(0);
	  }
      cv_wait(stack_lock, not_empty);
    }

    burger = stack_pop();
    num_consumed++;
    printf("Student %i ate burger %i\n", my_id, burger);

    mutex_unlock(stack_lock);
  }

  mutex_unlock(stack_lock);
  return 0;
}

int main()
{
  thread *allthreads = malloc(sizeof(thread) * (num_producers + num_consumers));

  for(i = 0; i < num_producers; i++)
    allthreads[i] = create_thread(producer, (void*)i, 1);
  for(j = 0; j < num_consumers; j++)
    allthreads[i+j] = create_thread(consumer, (void*)i, 1);


  //wait on all threads.
  for(i = 0; i < num_producers + num_consumers; i++)
    thread_join(allthreads[i]);  
}


alternate ending:

while(true)
{
  mutex_lock(stack_lock);
  if(num_consumed == burgers_to_make)
    exit(0); //terminate the program.
  mutex_unlock(stack_lock);
  thread_yield();
}

Important note: If your stack had a max height, then you also needed
a *SECOND* condition variable that was named not_full which is 
signaled each time a consumer eats one..









PROJECT 3 SYSTEM SET UP:

- note that we're using /cse451/projects/FC4-451-2Disk.tar.bz2 this time
 ** this image is persistent!

How to get your setup compiling:

~$ cd /cse451/username
/cse451/username$ mkdir proj4
/cse451/username$ cd proj4
/cse451/username/proj4$ cp /cse451/projects/linux-2.6.13.2-cse451fs.tar.bz2 .
/cse451/username/proj4$ tar vjxf linux-2.6.13.2-cse451fs.tar.bz2
(wait for it to unpack)
/cse451/username/proj4$ cp /cse451/projects/projFS.tar.bz2 .
/cse451/username/proj4$ tar vjxf projFS.tar.bz2
(wait for it to unpack)
/cse451/username/proj4$ ls
linux-2.6.13.2/     projFS/
(and the tar files)
/cse451/username/proj4$ cd linux-2.6.13.2/fs
/cse451/username/proj4/linux-2.6.13.2/fs$ ln -s ../../projFS/cse451_2.6/ cse451fs
/cse451/username/proj4/linux-2.6.13.2/fs$ ls -la cse*
lrwxrwxrwx 1 ak grad_cs 24 Feb 21 21:19 cse451fs -> ../../projFS/cse451_2.6/

To build mk451fs:
$ cd /cse451/username/proj4/projFS/mkfs
$ make
(This will build 'mk451fs')

To build the kernel (arch/i386/boot/bzImage) and cse451fs.ko:
$ cd /cse451/username/proj4/linux-2.6.13.2/
$ make
cse451fs.ko will be in /cse451/username/proj4/projFS/cse451_2.6
bzImage will be in /cse451/username/proj3/linux-2.6.13.2/arch/i386/boot/