Subversion Repositories HelenOS

/*

 * Copyright (c) 2001-2007 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.

 */

/** @addtogroup genericproc

 * @{

 */

/**

 * @file

 * @brief	Scheduler and load balancing.

 *

 * This file contains the scheduler and kcpulb kernel thread which

 * performs load-balancing of per-CPU run queues.

 */

#include <proc/scheduler.h>

#include <proc/thread.h>

#include <proc/task.h>

#include <mm/frame.h>

#include <mm/page.h>

#include <mm/as.h>

#include <time/timeout.h>

#include <time/delay.h>

#include <arch/asm.h>

#include <arch/faddr.h>

#include <arch/cycle.h>

#include <atomic.h>

#include <synch/spinlock.h>

#include <config.h>

#include <context.h>

#include <fpu_context.h>

#include <func.h>

#include <arch.h>

#include <adt/list.h>

#include <panic.h>

#include <cpu.h>

#include <print.h>

#include <debug.h>

static void before_task_runs(void);

static void before_thread_runs(void);

static void after_thread_ran(void);

static void scheduler_separated_stack(void);

atomic_t nrdy;	/**< Number of ready threads in the system. */

/** Carry out actions before new task runs. */

void before_task_runs(void)

{

	before_task_runs_arch();

}

/** Take actions before new thread runs.

 *

 * Perform actions that need to be

 * taken before the newly selected

 * tread is passed control.

 *

 * THREAD->lock is locked on entry

 *

 */

void before_thread_runs(void)

{

	before_thread_runs_arch();

#ifdef CONFIG_FPU_LAZY

	if(THREAD == CPU->fpu_owner) 

		fpu_enable();

	else

		fpu_disable(); 

#else

	fpu_enable();

	if (THREAD->fpu_context_exists)

		fpu_context_restore(THREAD->saved_fpu_context);

	else {

		fpu_init();

		THREAD->fpu_context_exists = 1;

	}

#endif

}

/** Take actions after THREAD had run.

 *

 * Perform actions that need to be

 * taken after the running thread

 * had been preempted by the scheduler.

 *

 * THREAD->lock is locked on entry

 *

 */

void after_thread_ran(void)

{

	after_thread_ran_arch();

}

#ifdef CONFIG_FPU_LAZY

void scheduler_fpu_lazy_request(void)

{

restart:

	fpu_enable();

	spinlock_lock(&CPU->lock);

	/* Save old context */

	if (CPU->fpu_owner != NULL) {  

		spinlock_lock(&CPU->fpu_owner->lock);

		fpu_context_save(CPU->fpu_owner->saved_fpu_context);

		/* don't prevent migration */

		CPU->fpu_owner->fpu_context_engaged = 0;

		spinlock_unlock(&CPU->fpu_owner->lock);

		CPU->fpu_owner = NULL;

	}

	spinlock_lock(&THREAD->lock);

	if (THREAD->fpu_context_exists) {

		fpu_context_restore(THREAD->saved_fpu_context);

	} else {

		/* Allocate FPU context */

		if (!THREAD->saved_fpu_context) {

			/* Might sleep */

			spinlock_unlock(&THREAD->lock);

			spinlock_unlock(&CPU->lock);

			THREAD->saved_fpu_context =

			    (fpu_context_t *) slab_alloc(fpu_context_slab, 0);

			/* We may have switched CPUs during slab_alloc */

			goto restart; 

		}

		fpu_init();

		THREAD->fpu_context_exists = 1;

	}

	CPU->fpu_owner = THREAD;

	THREAD->fpu_context_engaged = 1;

	spinlock_unlock(&THREAD->lock);

	spinlock_unlock(&CPU->lock);

}

#endif

/** Initialize scheduler

 *

 * Initialize kernel scheduler.

 *

 */

void scheduler_init(void)

{

}

/** Get thread to be scheduled

 *

 * Get the optimal thread to be scheduled

 * according to thread accounting and scheduler

 * policy.

 *

 * @return Thread to be scheduled.

 *

 */

static thread_t *find_best_thread(void)

{

	thread_t *t;

	runq_t *r;

	int i;

	ASSERT(CPU != NULL);

loop:

	interrupts_enable();

	if (atomic_get(&CPU->nrdy) == 0) {

		/*

		 * 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.

		 */

		/*

		 * An interrupt might occur right now and wake up a thread.

		 * In such case, the CPU will continue to go to sleep

		 * even though there is a runnable thread.

		 */

		 cpu_sleep();

		 goto loop;

	}

	interrupts_disable();

	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;

		}

		atomic_dec(&CPU->nrdy);

		atomic_dec(&nrdy);

		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->priority = i;	/* correct rq index */

		/*

		 * Clear the THREAD_FLAG_STOLEN flag so that t can be migrated

		 * when load balancing needs emerge.

		 */

		t->flags &= ~THREAD_FLAG_STOLEN;

		spinlock_unlock(&t->lock);

		return t;

	}

	goto loop;

}

/** Prevent rq starvation

 *

 * Prevent low priority threads from starving in rq's.

 *

 * When the function 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.

 *

 * @param start Threshold priority.

 *

 */

static 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

 *

 * The thread scheduling procedure.

 * Passes control directly to

 * scheduler_separated_stack().

 *

 */

void scheduler(void)

{

	volatile ipl_t ipl;

	ASSERT(CPU != NULL);

	ipl = interrupts_disable();

	if (atomic_get(&haltstate))

		halt();

	if (THREAD) {

		spinlock_lock(&THREAD->lock);

		/* Update thread accounting */

		THREAD->cycles += get_cycle() - THREAD->last_cycle;

#ifndef CONFIG_FPU_LAZY

		fpu_context_save(THREAD->saved_fpu_context);

#endif

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

			/*

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

			 */

			/* Save current CPU cycle */

			THREAD->last_cycle = get_cycle();

			spinlock_unlock(&THREAD->lock);

			interrupts_restore(THREAD->saved_context.ipl);

			return;

		}

		/*

		 * Interrupt priority level of preempted thread is recorded

		 * here to facilitate scheduler() invocations from

		 * interrupts_disable()'d code (e.g. waitq_sleep_timeout()). 

		 */

		THREAD->saved_context.ipl = ipl;

	}

	/*

	 * Through the 'THE' structure, we keep track of THREAD, TASK, CPU, VM

	 * and preemption counter. At this point THE could be coming either

	 * from THREAD's or CPU's stack.

	 */

	the_copy(THE, (the_t *) CPU->stack);

	/*

	 * 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);

	context_set(&CPU->saved_context, FADDR(scheduler_separated_stack),

	    (uintptr_t) CPU->stack, CPU_STACK_SIZE);

	context_restore(&CPU->saved_context);

	/* not reached */

}

/** Scheduler stack switch wrapper

 *

 * Second part of the scheduler() function

 * using new stack. Handling the actual context

 * switch to a new thread.

 *

 * Assume THREAD->lock is held.

 */

void scheduler_separated_stack(void)

{

	int priority;

	DEADLOCK_PROBE_INIT(p_joinwq);

	ASSERT(CPU != NULL);

	if (THREAD) {

		/* must be run after the switch to scheduler stack */

		after_thread_ran();

		switch (THREAD->state) {

		case Running:

			spinlock_unlock(&THREAD->lock);

			thread_ready(THREAD);

			break;

		case Exiting:

repeat:

			if (THREAD->detached) {

				thread_destroy(THREAD);

			} else {

				/*

				 * The thread structure is kept allocated until

				 * somebody calls thread_detach() on it.

				 */

				if (!spinlock_trylock(&THREAD->join_wq.lock)) {

					/*

					 * Avoid deadlock.

					 */

					spinlock_unlock(&THREAD->lock);

					delay(HZ);

					spinlock_lock(&THREAD->lock);

					DEADLOCK_PROBE(p_joinwq,

					    DEADLOCK_THRESHOLD);

					goto repeat;

				}

				_waitq_wakeup_unsafe(&THREAD->join_wq,

				    WAKEUP_FIRST);

				spinlock_unlock(&THREAD->join_wq.lock);

				THREAD->state = Lingering;

				spinlock_unlock(&THREAD->lock);

			}

			break;

		case Sleeping:

			/*

			 * Prefer the thread after it's woken up.

			 */

			THREAD->priority = -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%llu: unexpected state %s\n", THREAD->tid,

			    thread_states[THREAD->state]);

			break;

		}

		THREAD = NULL;

	}

	THREAD = find_best_thread();

	spinlock_lock(&THREAD->lock);

	priority = THREAD->priority;

	spinlock_unlock(&THREAD->lock);	

	relink_rq(priority);		

	/*

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

	 * avoided.

	 */

	if (TASK != THREAD->task) {

		as_t *as1 = NULL;

		as_t *as2;

		if (TASK) {

			spinlock_lock(&TASK->lock);

			as1 = TASK->as;

			spinlock_unlock(&TASK->lock);

		}

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

		as2 = THREAD->task->as;

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

		/*

		 * Note that it is possible for two tasks to share one address

		 * space.

		 */

		if (as1 != as2) {

			/*

			 * Both tasks and address spaces are different.

			 * Replace the old one with the new one.

			 */

			as_switch(as1, as2);

		}

		TASK = THREAD->task;

		before_task_runs();

	}

	spinlock_lock(&THREAD->lock);	

	THREAD->state = Running;

#ifdef SCHEDULER_VERBOSE

	printf("cpu%d: tid %llu (priority=%d, ticks=%llu, nrdy=%ld)\n",

	    CPU->id, THREAD->tid, THREAD->priority, THREAD->ticks,

	    atomic_get(&CPU->nrdy));

#endif	

	/*

	 * Some architectures provide late kernel PA2KA(identity)

	 * mapping in a page fault handler. However, the page fault

	 * handler uses the kernel stack of the running thread and

	 * therefore cannot be used to map it. The kernel stack, if

	 * necessary, is to be mapped in before_thread_runs(). This

	 * function must be executed before the switch to the new stack.

	 */

	before_thread_runs();

	/*

	 * Copy the knowledge of CPU, TASK, THREAD and preemption counter to

	 * thread's stack.

	 */

	the_copy(THE, (the_t *) THREAD->kstack);

	context_restore(&THREAD->saved_context);

	/* not reached */

}

#ifdef CONFIG_SMP

/** Load balancing thread

 *

 * SMP load balancing thread, supervising thread supplies

 * for the CPU it's wired to.

 *

 * @param arg Generic thread argument (unused).

 *

 */

void kcpulb(void *arg)

{

	thread_t *t;

	int count, average, j, k = 0;

	unsigned int i;

	ipl_t ipl;

	/*

	 * Detach kcpulb as nobody will call thread_join_timeout() on it.

	 */

	thread_detach(THREAD);

loop:

	/*

	 * Work in 1s intervals.

	 */

	thread_sleep(1);

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.

	 */

	average = atomic_get(&nrdy) / config.cpu_active + 1;

	count = average - atomic_get(&CPU->nrdy);

	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];

			/*

			 * Not interested in ourselves.

			 * Doesn't require interrupt disabling for kcpulb has

			 * THREAD_FLAG_WIRED.

			 */

			if (CPU == cpu)

				continue;

			if (atomic_get(&cpu->nrdy) <= average)

				continue;

			ipl = interrupts_disable();

			r = &cpu->rq[j];

			spinlock_lock(&r->lock);

			if (r->n == 0) {

				spinlock_unlock(&r->lock);

				interrupts_restore(ipl);

				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. We don't want to

				 * steal threads whose FPU context is still in

				 * CPU.

				 */

				spinlock_lock(&t->lock);

				if ((!(t->flags & (THREAD_FLAG_WIRED |

				    THREAD_FLAG_STOLEN))) &&

				    (!(t->fpu_context_engaged))) {

					/*

					 * Remove t from r.

					 */

					spinlock_unlock(&t->lock);

					atomic_dec(&cpu->nrdy);

					atomic_dec(&nrdy);

					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 %llu -> cpu%d, nrdy=%ld, "

				    "avg=%nd\n", CPU->id, t->tid, CPU->id,

				    atomic_get(&CPU->nrdy),

				    atomic_get(&nrdy) / config.cpu_active);

#endif

				t->flags |= THREAD_FLAG_STOLEN;

				t->state = Entering;

				spinlock_unlock(&t->lock);

				thread_ready(t);

				interrupts_restore(ipl);

				if (--count == 0)

					goto satisfied;

				/*

				 * We are not satisfied yet, focus on another

				 * CPU next time.

				 */

				k++;

				continue;

			}

			interrupts_restore(ipl);

		}

	}

	if (atomic_get(&CPU->nrdy)) {

		/*

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

		 */

		scheduler();

	} else {

		/*

		 * We failed to migrate a single thread.

		 * Give up this turn.

		 */

		goto loop;

	}

	goto not_satisfied;

satisfied:

	goto loop;

}

#endif /* CONFIG_SMP */

/** Print information about threads & scheduler queues */

void sched_print_list(void)

{

	ipl_t ipl;

	unsigned int cpu, i;

	runq_t *r;

	thread_t *t;

	link_t *cur;

	/* We are going to mess with scheduler structures,

	 * let's not be interrupted */

	ipl = interrupts_disable();

	for (cpu = 0; cpu < config.cpu_count; cpu++) {

		if (!cpus[cpu].active)

			continue;

		spinlock_lock(&cpus[cpu].lock);

		printf("cpu%d: address=%p, nrdy=%ld, needs_relink=%ld\n",

		    cpus[cpu].id, &cpus[cpu], atomic_get(&cpus[cpu].nrdy),

		    cpus[cpu].needs_relink);

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

			r = &cpus[cpu].rq[i];

			spinlock_lock(&r->lock);

			if (!r->n) {

				spinlock_unlock(&r->lock);

				continue;

			}

			printf("\trq[%d]: ", i);

			for (cur = r->rq_head.next; cur != &r->rq_head;

				cur = cur->next) {

				t = list_get_instance(cur, thread_t, rq_link);

				printf("%llu(%s) ", t->tid,

				    thread_states[t->state]);

			}

			printf("\n");

			spinlock_unlock(&r->lock);

		}

		spinlock_unlock(&cpus[cpu].lock);

	}

	interrupts_restore(ipl);

}

/** @}

 */