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/*

 * Copyright (C) 2001-2004 Jakub Jermar

 * All rights reserved.

 *

 * Redistribution and use in source and binary forms, with or without

 * modification, are permitted provided that the following conditions

 * are met:

 *

 * - Redistributions of source code must retain the above copyright

 *   notice, this list of conditions and the following disclaimer.

 * - Redistributions in binary form must reproduce the above copyright

 *   notice, this list of conditions and the following disclaimer in the

 *   documentation and/or other materials provided with the distribution.

 * - The name of the author may not be used to endorse or promote products

 *   derived from this software without specific prior written permission.

 *

 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR

 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES

 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.

 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,

 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT

 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,

 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY

 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT

 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF

 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

 */

#include <proc/scheduler.h>

#include <proc/thread.h>

#include <proc/task.h>

#include <cpu.h>

#include <mm/vm.h>

#include <config.h>

#include <context.h>

#include <func.h>

#include <arch.h>

#include <arch/asm.h>

#include <list.h>

#include <typedefs.h>

#include <mm/page.h>

#include <synch/spinlock.h>

#ifdef __SMP__

#include <arch/smp/atomic.h>

#endif /* __SMP__ */

/*

 * NOTE ON ATOMIC READS:

 * Some architectures cannot read __u32 atomically.

 * For that reason, all accesses to nrdy and the likes must be protected by spinlock.

 */

spinlock_t nrdylock;

volatile int nrdy;

void scheduler_init(void)

{

	spinlock_initialize(&nrdylock);

}

/* cpu_priority_high()'d */

struct thread *find_best_thread(void)

{

	thread_t *t;

	runq_t *r;

	int i, n;

loop:

	cpu_priority_high();

	spinlock_lock(&CPU->lock);

	n = CPU->nrdy;

	spinlock_unlock(&CPU->lock);

	cpu_priority_low();

	if (n == 0) {

		#ifdef __SMP__

		/*

		 * If the load balancing thread is not running, wake it up and

		 * set CPU-private flag that the kcpulb has been started.

		 */

		if (test_and_set(&CPU->kcpulbstarted) == 0) {

    			waitq_wakeup(&CPU->kcpulb_wq, 0);

			goto loop;

		}

		#endif /* __SMP__ */

		/*

		 * For there was nothing to run, the CPU goes to sleep

		 * until a hardware interrupt or an IPI comes.

		 * This improves energy saving and hyperthreading.

		 * On the other hand, several hardware interrupts can be ignored.

		 */

		 cpu_sleep();

		 goto loop;

	}

	cpu_priority_high();

	for (i = 0; i<RQ_COUNT; i++) {

		r = &CPU->rq[i];

		spinlock_lock(&r->lock);

		if (r->n == 0) {

			/*

			 * If this queue is empty, try a lower-priority queue.

			 */

			spinlock_unlock(&r->lock);

			continue;

		}

		spinlock_lock(&nrdylock);

		nrdy--;

		spinlock_unlock(&nrdylock);		

		spinlock_lock(&CPU->lock);

		CPU->nrdy--;

		spinlock_unlock(&CPU->lock);

		r->n--;

		/*

		 * Take the first thread from the queue.

		 */

		t = list_get_instance(r->rq_head.next, thread_t, rq_link);

		list_remove(&t->rq_link);

		spinlock_unlock(&r->lock);

		spinlock_lock(&t->lock);

		t->cpu = CPU;

		t->ticks = us2ticks((i+1)*10000);

		t->pri = i;	/* eventually correct rq index */

		/*

		 * Clear the X_STOLEN flag so that t can be migrated when load balancing needs emerge.

		 */

		t->flags &= ~X_STOLEN;

		spinlock_unlock(&t->lock);

		return t;

	}

	goto loop;

}

/*

 * This function prevents low priority threads from starving in rq's.

 * When it decides to relink rq's, it reconnects respective pointers

 * so that in result threads with 'pri' greater or equal 'start' are

 * moved to a higher-priority queue.

 */

void relink_rq(int start)

{

	link_t head;

	runq_t *r;

	int i, n;

	list_initialize(&head);

	spinlock_lock(&CPU->lock);

	if (CPU->needs_relink > NEEDS_RELINK_MAX) {

		for (i = start; i<RQ_COUNT-1; i++) {

			/* remember and empty rq[i + 1] */

			r = &CPU->rq[i + 1];

			spinlock_lock(&r->lock);

			list_concat(&head, &r->rq_head);

			n = r->n;

			r->n = 0;

			spinlock_unlock(&r->lock);

			/* append rq[i + 1] to rq[i] */

			r = &CPU->rq[i];

			spinlock_lock(&r->lock);

			list_concat(&r->rq_head, &head);

			r->n += n;

			spinlock_unlock(&r->lock);

		}

		CPU->needs_relink = 0;

	}

	spinlock_unlock(&CPU->lock);				

}

/*

 * The scheduler.

 */

void scheduler(void)

{

	volatile pri_t pri;

	pri = cpu_priority_high();

	if (haltstate)

		halt();

	if (THREAD) {

		spinlock_lock(&THREAD->lock);

		if (!context_save(&THREAD->saved_context)) {

			/*

			 * This is the place where threads leave scheduler();

			 */

			before_thread_runs();

		    	spinlock_unlock(&THREAD->lock);

			cpu_priority_restore(THREAD->saved_context.pri);

			return;

		}

		THREAD->saved_context.pri = pri;

	}

	/*

	 * We may not keep the old stack.

	 * Reason: If we kept the old stack and got blocked, for instance, in

	 * find_best_thread(), the old thread could get rescheduled by another

	 * CPU and overwrite the part of its own stack that was also used by

	 * the scheduler on this CPU.

	 *

	 * Moreover, we have to bypass the compiler-generated POP sequence

	 * which is fooled by SP being set to the very top of the stack.

	 * Therefore the scheduler() function continues in

	 * scheduler_separated_stack().

	 */

	context_save(&CPU->saved_context);

	CPU->saved_context.sp = (__address) &CPU->stack[CPU_STACK_SIZE-8];

	CPU->saved_context.pc = (__address) scheduler_separated_stack;

	context_restore(&CPU->saved_context);

	/* not reached */

}

void scheduler_separated_stack(void)

{

	int priority;

	if (THREAD) {

		switch (THREAD->state) {

		    case Running:

			    THREAD->state = Ready;

			    spinlock_unlock(&THREAD->lock);

			    thread_ready(THREAD);

			    break;

		    case Exiting:

			    frame_free((__address) THREAD->kstack);

			    if (THREAD->ustack) {

				    frame_free((__address) THREAD->ustack);

			    }

			    /*

			     * Detach from the containing task.

			     */

			    spinlock_lock(&TASK->lock);

			    list_remove(&THREAD->th_link);

			    spinlock_unlock(&TASK->lock);

			    spinlock_unlock(&THREAD->lock);

			    spinlock_lock(&threads_lock);

			    list_remove(&THREAD->threads_link);

			    spinlock_unlock(&threads_lock);

			    free(THREAD);

			    break;

		    case Sleeping:

			    /*

			     * Prefer the thread after it's woken up.

			     */

			    THREAD->pri = -1;

			    /*

			     * We need to release wq->lock which we locked in waitq_sleep().

			     * Address of wq->lock is kept in THREAD->sleep_queue.

			     */

			    spinlock_unlock(&THREAD->sleep_queue->lock);

			    /*

			     * Check for possible requests for out-of-context invocation.

			     */

			    if (THREAD->call_me) {

				    THREAD->call_me(THREAD->call_me_with);

				    THREAD->call_me = NULL;

				    THREAD->call_me_with = NULL;

			    }

			    spinlock_unlock(&THREAD->lock);

			    break;

		    default:

			    /*

			     * Entering state is unexpected.

			     */

			    panic("tid%d: unexpected state %s\n", THREAD->tid, thread_states[THREAD->state]);

			    break;

		}

		THREAD = NULL;

	}

	THREAD = find_best_thread();

	spinlock_lock(&THREAD->lock);

	priority = THREAD->pri;

	spinlock_unlock(&THREAD->lock);	

	relink_rq(priority);		

	spinlock_lock(&THREAD->lock);	

	/*

	 * If both the old and the new task are the same, lots of work is avoided.

	 */

	if (TASK != THREAD->task) {

		vm_t *m1 = NULL;

		vm_t *m2;

		if (TASK) {

			spinlock_lock(&TASK->lock);

			m1 = TASK->vm;

			spinlock_unlock(&TASK->lock);

		}

		spinlock_lock(&THREAD->task->lock);

		m2 = THREAD->task->vm;

		spinlock_unlock(&THREAD->task->lock);

		/*

		 * Note that it is possible for two tasks to share one vm mapping.

		 */

		if (m1 != m2) {

			/*

			 * Both tasks and vm mappings are different.

			 * Replace the old one with the new one.

			 */

			if (m1) {

				vm_uninstall(m1);

			}

			vm_install(m2);

		}

		TASK = THREAD->task;	

	}

	THREAD->state = Running;

	#ifdef SCHEDULER_VERBOSE

	printf("cpu%d: tid %d (pri=%d,ticks=%d,nrdy=%d)\n", CPU->id, THREAD->tid, THREAD->pri, THREAD->ticks, CPU->nrdy);

	#endif	

	context_restore(&THREAD->saved_context);

	/* not reached */

}

#ifdef __SMP__

/*

 * This is the load balancing thread. 

 * It supervises thread supplies for the CPU it's wired to.

 */

void kcpulb(void *arg)

{

	thread_t *t;

	int count, i, j, k = 0;

	pri_t pri;

loop:

	/*

	 * Sleep until there's some work to do.

	 */

	waitq_sleep(&CPU->kcpulb_wq);

not_satisfied:

	/*

	 * Calculate the number of threads that will be migrated/stolen from

	 * other CPU's. Note that situation can have changed between two

	 * passes. Each time get the most up to date counts.

	 */

	pri = cpu_priority_high();

	spinlock_lock(&CPU->lock);

	count = nrdy / config.cpu_active;

	count -= CPU->nrdy;

	spinlock_unlock(&CPU->lock);

	cpu_priority_restore(pri);

	if (count <= 0)

		goto satisfied;

	/*

	 * Searching least priority queues on all CPU's first and most priority queues on all CPU's last.

	 */

	for (j=RQ_COUNT-1; j >= 0; j--) {

		for (i=0; i < config.cpu_active; i++) {

			link_t *l;

			runq_t *r;

			cpu_t *cpu;

			cpu = &cpus[(i + k) % config.cpu_active];

			r = &cpu->rq[j];

			/*

			 * Not interested in ourselves.

			 * Doesn't require interrupt disabling for kcpulb is X_WIRED.

			 */

			if (CPU == cpu)

				continue;

restart:		pri = cpu_priority_high();

			spinlock_lock(&r->lock);

			if (r->n == 0) {

				spinlock_unlock(&r->lock);

				cpu_priority_restore(pri);

				continue;

			}

			t = NULL;

			l = r->rq_head.prev;	/* search rq from the back */

			while (l != &r->rq_head) {

				t = list_get_instance(l, thread_t, rq_link);

				/*

		    		 * We don't want to steal CPU-wired threads neither threads already stolen.

				 * The latter prevents threads from migrating between CPU's without ever being run.

		        	 */

				spinlock_lock(&t->lock);

				if (!(t->flags & (X_WIRED | X_STOLEN))) {

					/*

					 * Remove t from r.

					 */

					spinlock_unlock(&t->lock);

					/*

					 * Here we have to avoid deadlock with relink_rq(),

					 * because it locks cpu and r in a different order than we do.

					 */

					if (!spinlock_trylock(&cpu->lock)) {

						/* Release all locks and try again. */ 

						spinlock_unlock(&r->lock);

						cpu_priority_restore(pri);

						goto restart;

					}

					cpu->nrdy--;

					spinlock_unlock(&cpu->lock);

					spinlock_lock(&nrdylock);

					nrdy--;

					spinlock_unlock(&nrdylock);					

			    		r->n--;

					list_remove(&t->rq_link);

					break;

				}

				spinlock_unlock(&t->lock);

				l = l->prev;

				t = NULL;

			}

			spinlock_unlock(&r->lock);

			if (t) {

				/*

				 * Ready t on local CPU

				 */

				spinlock_lock(&t->lock);

				#ifdef KCPULB_VERBOSE

				printf("kcpulb%d: TID %d -> cpu%d, nrdy=%d, avg=%d\n", CPU->id, t->tid, CPU->id, CPU->nrdy, nrdy / config.cpu_active);

				#endif

				t->flags |= X_STOLEN;

				spinlock_unlock(&t->lock);

				thread_ready(t);

				cpu_priority_restore(pri);

				if (--count == 0)

					goto satisfied;

				/*

                    		 * We are not satisfied yet, focus on another CPU next time.

				 */

				k++;

				continue;

			}

			cpu_priority_restore(pri);

		}

	}

	if (CPU->nrdy) {

		/*

		 * Be a little bit light-weight and let migrated threads run.

		 */

		scheduler();

	} 

	else {

		/*

		 * We failed to migrate a single thread.

		 * Something more sophisticated should be done.

		 */

		scheduler();

	}

	goto not_satisfied;

satisfied:

	/*

	 * Tell find_best_thread() to wake us up later again.

	 */

	CPU->kcpulbstarted = 0;

	goto loop;

}

#endif /* __SMP__ */