WebSVN – HelenOS-historic – Diff – /kernel/trunk/generic/src/proc/scheduler.c

 /*
  * 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 <mm/frame.h>
 #include <mm/page.h>
 #include <mm/as.h>
 #include <arch/asm.h>
 #include <arch/faddr.h>
 #include <arch/atomic.h>
 #include <synch/spinlock.h>
 #include <config.h>
 #include <context.h>
 #include <func.h>
 #include <arch.h>
 #include <adt/list.h>
 #include <panic.h>
 #include <typedefs.h>
 #include <cpu.h>
 #include <print.h>
 #include <debug.h>
-atomic_t nrdy;
+static void scheduler_separated_stack(void);
+atomic_t nrdy;  /**< Number of ready threads in the system. */
 /** 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
+    #ifdef CONFIG_FPU_LAZY
     if(THREAD==CPU->fpu_owner)
         fpu_enable();
     else
         fpu_disable();
-#else
+    #else
     fpu_enable();
     if (THREAD->fpu_context_exists)
         fpu_context_restore(&(THREAD->saved_fpu_context));
     else {
         fpu_init(&(THREAD->saved_fpu_context));
         THREAD->fpu_context_exists=1;
+    }
-#endif
+    #endif
+}
-/** Take actions after old thread ran.
+/** Take actions after THREAD had run.
+ *
  * Perform actions that need to be
  * taken after the running thread
- * was preempted by the scheduler.
+ * 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)
+{
     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);
+    }
     spinlock_lock(&THREAD->lock);
-    if (THREAD->fpu_context_exists)
+    if (THREAD->fpu_context_exists) {
         fpu_context_restore(&THREAD->saved_fpu_context);
-    else {
+    } else {
         fpu_init(&(THREAD->saved_fpu_context));
         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();
-    i = 0;
-    for (; i<RQ_COUNT; i++) {
+    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;    /* eventually correct rq index */
+        t->priority = i;    /* 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;
+}
 /** 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);
+        #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();
+             */
+            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), (__address) 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.
  */
-static void scheduler_separated_stack(void)
+void scheduler_separated_stack(void)
+{
     int priority;
     ASSERT(CPU != NULL);
     if (THREAD) {
-        /* must be run after switch to scheduler stack */
+        /* must be run after the switch to scheduler stack */
         after_thread_ran();
         switch (THREAD->state) {
             case Running:
             THREAD->state = Ready;
             spinlock_unlock(&THREAD->lock);
             thread_ready(THREAD);
             break;
             case Exiting:
             thread_destroy(THREAD);
             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%d: 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);
     spinlock_lock(&THREAD->lock);
     /*
      * 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;
+    }
     THREAD->state = Running;
     #ifdef SCHEDULER_VERBOSE
     printf("cpu%d: tid %d (priority=%d,ticks=%d,nrdy=%d)\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 */
+}
-/** 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);
-#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();
-             */
-            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), (__address) CPU->stack, CPU_STACK_SIZE);
-    context_restore(&CPU->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, i, j, k = 0;
     ipl_t ipl;
 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 is X_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 & (X_WIRED | X_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 %d -> cpu%d, nrdy=%d, avg=%d\n", CPU->id, t->tid, CPU->id, atomic_get(&CPU->nrdy), atomic_get(&nrdy) / config.cpu_active);
                 #endif
                 t->flags |= X_STOLEN;
                 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;
     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();
-    printf("*********** Scheduler dump ***********\n");
+    printf("Scheduler dump:\n");
     for (cpu=0;cpu < config.cpu_count; cpu++) {
         if (!cpus[cpu].active)
             continue;
         spinlock_lock(&cpus[cpu].lock);
-        printf("cpu%d: nrdy: %d needs_relink: %d\n",
+        printf("cpu%d: nrdy: %d, needs_relink: %d\n",
                cpus[cpu].id, 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);
+            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("%d(%s) ", t->tid,
                        thread_states[t->state]);
+            }
             printf("\n");
             spinlock_unlock(&r->lock);
+        }
         spinlock_unlock(&cpus[cpu].lock);
+    }
     interrupts_restore(ipl);
+}

Subversion Repositories HelenOS-historic

(root)/kernel/trunk/generic/src/proc/scheduler.c @ 1757 – Rev 897 → 898