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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 before_thread_runs(void)

{

    before_thread_runs_arch();

    fpu_context_restore();

}

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__ */