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  1. /*
  2.  * Copyright (C) 2001-2004 Jakub Jermar
  3.  * All rights reserved.
  4.  *
  5.  * Redistribution and use in source and binary forms, with or without
  6.  * modification, are permitted provided that the following conditions
  7.  * are met:
  8.  *
  9.  * - Redistributions of source code must retain the above copyright
  10.  *   notice, this list of conditions and the following disclaimer.
  11.  * - Redistributions in binary form must reproduce the above copyright
  12.  *   notice, this list of conditions and the following disclaimer in the
  13.  *   documentation and/or other materials provided with the distribution.
  14.  * - The name of the author may not be used to endorse or promote products
  15.  *   derived from this software without specific prior written permission.
  16.  *
  17.  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
  18.  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
  19.  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
  20.  * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
  21.  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
  22.  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  23.  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  24.  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  25.  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
  26.  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  27.  */
  28.  
  29. /** @addtogroup genericproc
  30.  * @{
  31.  */
  32.  
  33. /**
  34.  * @file
  35.  * @brief   Scheduler and load balancing.
  36.  *
  37.  * This file contains the scheduler and kcpulb kernel thread which
  38.  * performs load-balancing of per-CPU run queues.
  39.  */
  40.  
  41. #include <proc/scheduler.h>
  42. #include <proc/thread.h>
  43. #include <proc/task.h>
  44. #include <mm/frame.h>
  45. #include <mm/page.h>
  46. #include <mm/as.h>
  47. #include <time/delay.h>
  48. #include <arch/asm.h>
  49. #include <arch/faddr.h>
  50. #include <atomic.h>
  51. #include <synch/spinlock.h>
  52. #include <config.h>
  53. #include <context.h>
  54. #include <func.h>
  55. #include <arch.h>
  56. #include <adt/list.h>
  57. #include <panic.h>
  58. #include <typedefs.h>
  59. #include <cpu.h>
  60. #include <print.h>
  61. #include <debug.h>
  62.  
  63. static void before_task_runs(void);
  64. static void before_thread_runs(void);
  65. static void after_thread_ran(void);
  66. static void scheduler_separated_stack(void);
  67.  
  68. atomic_t nrdy;  /**< Number of ready threads in the system. */
  69.  
  70. /** Carry out actions before new task runs. */
  71. void before_task_runs(void)
  72. {
  73.     before_task_runs_arch();
  74. }
  75.  
  76. /** Take actions before new thread runs.
  77.  *
  78.  * Perform actions that need to be
  79.  * taken before the newly selected
  80.  * tread is passed control.
  81.  *
  82.  * THREAD->lock is locked on entry
  83.  *
  84.  */
  85. void before_thread_runs(void)
  86. {
  87.     before_thread_runs_arch();
  88. #ifdef CONFIG_FPU_LAZY
  89.     if(THREAD == CPU->fpu_owner)
  90.         fpu_enable();
  91.     else
  92.         fpu_disable();
  93. #else
  94.     fpu_enable();
  95.     if (THREAD->fpu_context_exists)
  96.         fpu_context_restore(THREAD->saved_fpu_context);
  97.     else {
  98.         fpu_init();
  99.         THREAD->fpu_context_exists = 1;
  100.     }
  101. #endif
  102. }
  103.  
  104. /** Take actions after THREAD had run.
  105.  *
  106.  * Perform actions that need to be
  107.  * taken after the running thread
  108.  * had been preempted by the scheduler.
  109.  *
  110.  * THREAD->lock is locked on entry
  111.  *
  112.  */
  113. void after_thread_ran(void)
  114. {
  115.     after_thread_ran_arch();
  116. }
  117.  
  118. #ifdef CONFIG_FPU_LAZY
  119. void scheduler_fpu_lazy_request(void)
  120. {
  121. restart:
  122.     fpu_enable();
  123.     spinlock_lock(&CPU->lock);
  124.  
  125.     /* Save old context */
  126.     if (CPU->fpu_owner != NULL) {  
  127.         spinlock_lock(&CPU->fpu_owner->lock);
  128.         fpu_context_save(CPU->fpu_owner->saved_fpu_context);
  129.         /* don't prevent migration */
  130.         CPU->fpu_owner->fpu_context_engaged = 0;
  131.         spinlock_unlock(&CPU->fpu_owner->lock);
  132.         CPU->fpu_owner = NULL;
  133.     }
  134.  
  135.     spinlock_lock(&THREAD->lock);
  136.     if (THREAD->fpu_context_exists) {
  137.         fpu_context_restore(THREAD->saved_fpu_context);
  138.     } else {
  139.         /* Allocate FPU context */
  140.         if (!THREAD->saved_fpu_context) {
  141.             /* Might sleep */
  142.             spinlock_unlock(&THREAD->lock);
  143.             spinlock_unlock(&CPU->lock);
  144.             THREAD->saved_fpu_context = slab_alloc(fpu_context_slab, 0);
  145.             /* We may have switched CPUs during slab_alloc */
  146.             goto restart;
  147.         }
  148.         fpu_init();
  149.         THREAD->fpu_context_exists = 1;
  150.     }
  151.     CPU->fpu_owner = THREAD;
  152.     THREAD->fpu_context_engaged = 1;
  153.     spinlock_unlock(&THREAD->lock);
  154.  
  155.     spinlock_unlock(&CPU->lock);
  156. }
  157. #endif
  158.  
  159. /** Initialize scheduler
  160.  *
  161.  * Initialize kernel scheduler.
  162.  *
  163.  */
  164. void scheduler_init(void)
  165. {
  166. }
  167.  
  168. /** Get thread to be scheduled
  169.  *
  170.  * Get the optimal thread to be scheduled
  171.  * according to thread accounting and scheduler
  172.  * policy.
  173.  *
  174.  * @return Thread to be scheduled.
  175.  *
  176.  */
  177. static thread_t *find_best_thread(void)
  178. {
  179.     thread_t *t;
  180.     runq_t *r;
  181.     int i;
  182.  
  183.     ASSERT(CPU != NULL);
  184.  
  185. loop:
  186.     interrupts_enable();
  187.    
  188.     if (atomic_get(&CPU->nrdy) == 0) {
  189.         /*
  190.          * For there was nothing to run, the CPU goes to sleep
  191.          * until a hardware interrupt or an IPI comes.
  192.          * This improves energy saving and hyperthreading.
  193.          */
  194.  
  195.         /*
  196.          * An interrupt might occur right now and wake up a thread.
  197.          * In such case, the CPU will continue to go to sleep
  198.          * even though there is a runnable thread.
  199.          */
  200.  
  201.          cpu_sleep();
  202.          goto loop;
  203.     }
  204.  
  205.     interrupts_disable();
  206.    
  207.     for (i = 0; i<RQ_COUNT; i++) {
  208.         r = &CPU->rq[i];
  209.         spinlock_lock(&r->lock);
  210.         if (r->n == 0) {
  211.             /*
  212.              * If this queue is empty, try a lower-priority queue.
  213.              */
  214.             spinlock_unlock(&r->lock);
  215.             continue;
  216.         }
  217.  
  218.         atomic_dec(&CPU->nrdy);
  219.         atomic_dec(&nrdy);
  220.         r->n--;
  221.  
  222.         /*
  223.          * Take the first thread from the queue.
  224.          */
  225.         t = list_get_instance(r->rq_head.next, thread_t, rq_link);
  226.         list_remove(&t->rq_link);
  227.  
  228.         spinlock_unlock(&r->lock);
  229.  
  230.         spinlock_lock(&t->lock);
  231.         t->cpu = CPU;
  232.  
  233.         t->ticks = us2ticks((i+1)*10000);
  234.         t->priority = i;    /* correct rq index */
  235.  
  236.         /*
  237.          * Clear the THREAD_FLAG_STOLEN flag so that t can be migrated
  238.          * when load balancing needs emerge.
  239.          */
  240.         t->flags &= ~THREAD_FLAG_STOLEN;
  241.         spinlock_unlock(&t->lock);
  242.  
  243.         return t;
  244.     }
  245.     goto loop;
  246.  
  247. }
  248.  
  249. /** Prevent rq starvation
  250.  *
  251.  * Prevent low priority threads from starving in rq's.
  252.  *
  253.  * When the function decides to relink rq's, it reconnects
  254.  * respective pointers so that in result threads with 'pri'
  255.  * greater or equal start are moved to a higher-priority queue.
  256.  *
  257.  * @param start Threshold priority.
  258.  *
  259.  */
  260. static void relink_rq(int start)
  261. {
  262.     link_t head;
  263.     runq_t *r;
  264.     int i, n;
  265.  
  266.     list_initialize(&head);
  267.     spinlock_lock(&CPU->lock);
  268.     if (CPU->needs_relink > NEEDS_RELINK_MAX) {
  269.         for (i = start; i<RQ_COUNT-1; i++) {
  270.             /* remember and empty rq[i + 1] */
  271.             r = &CPU->rq[i + 1];
  272.             spinlock_lock(&r->lock);
  273.             list_concat(&head, &r->rq_head);
  274.             n = r->n;
  275.             r->n = 0;
  276.             spinlock_unlock(&r->lock);
  277.        
  278.             /* append rq[i + 1] to rq[i] */
  279.             r = &CPU->rq[i];
  280.             spinlock_lock(&r->lock);
  281.             list_concat(&r->rq_head, &head);
  282.             r->n += n;
  283.             spinlock_unlock(&r->lock);
  284.         }
  285.         CPU->needs_relink = 0;
  286.     }
  287.     spinlock_unlock(&CPU->lock);
  288.  
  289. }
  290.  
  291. /** The scheduler
  292.  *
  293.  * The thread scheduling procedure.
  294.  * Passes control directly to
  295.  * scheduler_separated_stack().
  296.  *
  297.  */
  298. void scheduler(void)
  299. {
  300.     volatile ipl_t ipl;
  301.  
  302.     ASSERT(CPU != NULL);
  303.  
  304.     ipl = interrupts_disable();
  305.  
  306.     if (atomic_get(&haltstate))
  307.         halt();
  308.    
  309.     if (THREAD) {
  310.         spinlock_lock(&THREAD->lock);
  311. #ifndef CONFIG_FPU_LAZY
  312.         fpu_context_save(THREAD->saved_fpu_context);
  313. #endif
  314.         if (!context_save(&THREAD->saved_context)) {
  315.             /*
  316.              * This is the place where threads leave scheduler();
  317.              */
  318.             spinlock_unlock(&THREAD->lock);
  319.             interrupts_restore(THREAD->saved_context.ipl);
  320.            
  321.             return;
  322.         }
  323.  
  324.         /*
  325.          * Interrupt priority level of preempted thread is recorded here
  326.          * to facilitate scheduler() invocations from interrupts_disable()'d
  327.          * code (e.g. waitq_sleep_timeout()).
  328.          */
  329.         THREAD->saved_context.ipl = ipl;
  330.     }
  331.  
  332.     /*
  333.      * Through the 'THE' structure, we keep track of THREAD, TASK, CPU, VM
  334.      * and preemption counter. At this point THE could be coming either
  335.      * from THREAD's or CPU's stack.
  336.      */
  337.     the_copy(THE, (the_t *) CPU->stack);
  338.  
  339.     /*
  340.      * We may not keep the old stack.
  341.      * Reason: If we kept the old stack and got blocked, for instance, in
  342.      * find_best_thread(), the old thread could get rescheduled by another
  343.      * CPU and overwrite the part of its own stack that was also used by
  344.      * the scheduler on this CPU.
  345.      *
  346.      * Moreover, we have to bypass the compiler-generated POP sequence
  347.      * which is fooled by SP being set to the very top of the stack.
  348.      * Therefore the scheduler() function continues in
  349.      * scheduler_separated_stack().
  350.      */
  351.     context_save(&CPU->saved_context);
  352.     context_set(&CPU->saved_context, FADDR(scheduler_separated_stack),
  353.         (uintptr_t) CPU->stack, CPU_STACK_SIZE);
  354.     context_restore(&CPU->saved_context);
  355.     /* not reached */
  356. }
  357.  
  358. /** Scheduler stack switch wrapper
  359.  *
  360.  * Second part of the scheduler() function
  361.  * using new stack. Handling the actual context
  362.  * switch to a new thread.
  363.  *
  364.  * Assume THREAD->lock is held.
  365.  */
  366. void scheduler_separated_stack(void)
  367. {
  368.     int priority;
  369.    
  370.     ASSERT(CPU != NULL);
  371.    
  372.     if (THREAD) {
  373.         /* must be run after the switch to scheduler stack */
  374.         after_thread_ran();
  375.  
  376.         switch (THREAD->state) {
  377.         case Running:
  378.             spinlock_unlock(&THREAD->lock);
  379.             thread_ready(THREAD);
  380.             break;
  381.  
  382.         case Exiting:
  383. repeat:
  384.                 if (THREAD->detached) {
  385.                 thread_destroy(THREAD);
  386.             } else {
  387.                 /*
  388.                  * The thread structure is kept allocated until somebody
  389.                  * calls thread_detach() on it.
  390.                  */
  391.                 if (!spinlock_trylock(&THREAD->join_wq.lock)) {
  392.                     /*
  393.                      * Avoid deadlock.
  394.                      */
  395.                     spinlock_unlock(&THREAD->lock);
  396.                     delay(10);
  397.                     spinlock_lock(&THREAD->lock);
  398.                     goto repeat;
  399.                 }
  400.                 _waitq_wakeup_unsafe(&THREAD->join_wq, false);
  401.                 spinlock_unlock(&THREAD->join_wq.lock);
  402.                
  403.                 THREAD->state = Undead;
  404.                 spinlock_unlock(&THREAD->lock);
  405.             }
  406.             break;
  407.            
  408.         case Sleeping:
  409.             /*
  410.              * Prefer the thread after it's woken up.
  411.              */
  412.             THREAD->priority = -1;
  413.  
  414.             /*
  415.              * We need to release wq->lock which we locked in waitq_sleep().
  416.              * Address of wq->lock is kept in THREAD->sleep_queue.
  417.              */
  418.             spinlock_unlock(&THREAD->sleep_queue->lock);
  419.  
  420.             /*
  421.              * Check for possible requests for out-of-context invocation.
  422.              */
  423.             if (THREAD->call_me) {
  424.                 THREAD->call_me(THREAD->call_me_with);
  425.                 THREAD->call_me = NULL;
  426.                 THREAD->call_me_with = NULL;
  427.             }
  428.  
  429.             spinlock_unlock(&THREAD->lock);
  430.  
  431.             break;
  432.  
  433.         default:
  434.             /*
  435.              * Entering state is unexpected.
  436.              */
  437.             panic("tid%d: unexpected state %s\n", THREAD->tid, thread_states[THREAD->state]);
  438.             break;
  439.         }
  440.  
  441.         THREAD = NULL;
  442.     }
  443.  
  444.     THREAD = find_best_thread();
  445.    
  446.     spinlock_lock(&THREAD->lock);
  447.     priority = THREAD->priority;
  448.     spinlock_unlock(&THREAD->lock);
  449.  
  450.     relink_rq(priority);       
  451.  
  452.     /*
  453.      * If both the old and the new task are the same, lots of work is avoided.
  454.      */
  455.     if (TASK != THREAD->task) {
  456.         as_t *as1 = NULL;
  457.         as_t *as2;
  458.  
  459.         if (TASK) {
  460.             spinlock_lock(&TASK->lock);
  461.             as1 = TASK->as;
  462.             spinlock_unlock(&TASK->lock);
  463.         }
  464.  
  465.         spinlock_lock(&THREAD->task->lock);
  466.         as2 = THREAD->task->as;
  467.         spinlock_unlock(&THREAD->task->lock);
  468.        
  469.         /*
  470.          * Note that it is possible for two tasks to share one address space.
  471.          */
  472.         if (as1 != as2) {
  473.             /*
  474.              * Both tasks and address spaces are different.
  475.              * Replace the old one with the new one.
  476.              */
  477.             as_switch(as1, as2);
  478.         }
  479.         TASK = THREAD->task;
  480.         before_task_runs();
  481.     }
  482.  
  483.     spinlock_lock(&THREAD->lock);  
  484.     THREAD->state = Running;
  485.  
  486. #ifdef SCHEDULER_VERBOSE
  487.     printf("cpu%d: tid %d (priority=%d,ticks=%lld,nrdy=%ld)\n",
  488.         CPU->id, THREAD->tid, THREAD->priority, THREAD->ticks, atomic_get(&CPU->nrdy));
  489. #endif 
  490.  
  491.     /*
  492.      * Some architectures provide late kernel PA2KA(identity)
  493.      * mapping in a page fault handler. However, the page fault
  494.      * handler uses the kernel stack of the running thread and
  495.      * therefore cannot be used to map it. The kernel stack, if
  496.      * necessary, is to be mapped in before_thread_runs(). This
  497.      * function must be executed before the switch to the new stack.
  498.      */
  499.     before_thread_runs();
  500.  
  501.     /*
  502.      * Copy the knowledge of CPU, TASK, THREAD and preemption counter to thread's stack.
  503.      */
  504.     the_copy(THE, (the_t *) THREAD->kstack);
  505.    
  506.     context_restore(&THREAD->saved_context);
  507.     /* not reached */
  508. }
  509.  
  510. #ifdef CONFIG_SMP
  511. /** Load balancing thread
  512.  *
  513.  * SMP load balancing thread, supervising thread supplies
  514.  * for the CPU it's wired to.
  515.  *
  516.  * @param arg Generic thread argument (unused).
  517.  *
  518.  */
  519. void kcpulb(void *arg)
  520. {
  521.     thread_t *t;
  522.     int count, average, i, j, k = 0;
  523.     ipl_t ipl;
  524.  
  525.     /*
  526.      * Detach kcpulb as nobody will call thread_join_timeout() on it.
  527.      */
  528.     thread_detach(THREAD);
  529.    
  530. loop:
  531.     /*
  532.      * Work in 1s intervals.
  533.      */
  534.     thread_sleep(1);
  535.  
  536. not_satisfied:
  537.     /*
  538.      * Calculate the number of threads that will be migrated/stolen from
  539.      * other CPU's. Note that situation can have changed between two
  540.      * passes. Each time get the most up to date counts.
  541.      */
  542.     average = atomic_get(&nrdy) / config.cpu_active + 1;
  543.     count = average - atomic_get(&CPU->nrdy);
  544.  
  545.     if (count <= 0)
  546.         goto satisfied;
  547.  
  548.     /*
  549.      * Searching least priority queues on all CPU's first and most priority queues on all CPU's last.
  550.      */
  551.     for (j=RQ_COUNT-1; j >= 0; j--) {
  552.         for (i=0; i < config.cpu_active; i++) {
  553.             link_t *l;
  554.             runq_t *r;
  555.             cpu_t *cpu;
  556.  
  557.             cpu = &cpus[(i + k) % config.cpu_active];
  558.  
  559.             /*
  560.              * Not interested in ourselves.
  561.              * Doesn't require interrupt disabling for kcpulb has THREAD_FLAG_WIRED.
  562.              */
  563.             if (CPU == cpu)
  564.                 continue;
  565.             if (atomic_get(&cpu->nrdy) <= average)
  566.                 continue;
  567.  
  568.             ipl = interrupts_disable();
  569.             r = &cpu->rq[j];
  570.             spinlock_lock(&r->lock);
  571.             if (r->n == 0) {
  572.                 spinlock_unlock(&r->lock);
  573.                 interrupts_restore(ipl);
  574.                 continue;
  575.             }
  576.        
  577.             t = NULL;
  578.             l = r->rq_head.prev;    /* search rq from the back */
  579.             while (l != &r->rq_head) {
  580.                 t = list_get_instance(l, thread_t, rq_link);
  581.                 /*
  582.                  * We don't want to steal CPU-wired threads neither threads already
  583.                  * stolen. The latter prevents threads from migrating between CPU's
  584.                  * without ever being run. We don't want to steal threads whose FPU
  585.                  * context is still in CPU.
  586.                  */
  587.                 spinlock_lock(&t->lock);
  588.                 if ((!(t->flags & (THREAD_FLAG_WIRED | THREAD_FLAG_STOLEN))) &&
  589.                     (!(t->fpu_context_engaged)) ) {
  590.                     /*
  591.                      * Remove t from r.
  592.                      */
  593.                     spinlock_unlock(&t->lock);
  594.                    
  595.                     atomic_dec(&cpu->nrdy);
  596.                     atomic_dec(&nrdy);
  597.  
  598.                     r->n--;
  599.                     list_remove(&t->rq_link);
  600.  
  601.                     break;
  602.                 }
  603.                 spinlock_unlock(&t->lock);
  604.                 l = l->prev;
  605.                 t = NULL;
  606.             }
  607.             spinlock_unlock(&r->lock);
  608.  
  609.             if (t) {
  610.                 /*
  611.                  * Ready t on local CPU
  612.                  */
  613.                 spinlock_lock(&t->lock);
  614. #ifdef KCPULB_VERBOSE
  615.                 printf("kcpulb%d: TID %d -> cpu%d, nrdy=%ld, avg=%nd\n",
  616.                     CPU->id, t->tid, CPU->id, atomic_get(&CPU->nrdy),
  617.                     atomic_get(&nrdy) / config.cpu_active);
  618. #endif
  619.                 t->flags |= THREAD_FLAG_STOLEN;
  620.                 t->state = Entering;
  621.                 spinlock_unlock(&t->lock);
  622.    
  623.                 thread_ready(t);
  624.  
  625.                 interrupts_restore(ipl);
  626.    
  627.                 if (--count == 0)
  628.                     goto satisfied;
  629.                    
  630.                 /*
  631.                  * We are not satisfied yet, focus on another CPU next time.
  632.                  */
  633.                 k++;
  634.                
  635.                 continue;
  636.             }
  637.             interrupts_restore(ipl);
  638.         }
  639.     }
  640.  
  641.     if (atomic_get(&CPU->nrdy)) {
  642.         /*
  643.          * Be a little bit light-weight and let migrated threads run.
  644.          */
  645.         scheduler();
  646.     } else {
  647.         /*
  648.          * We failed to migrate a single thread.
  649.          * Give up this turn.
  650.          */
  651.         goto loop;
  652.     }
  653.        
  654.     goto not_satisfied;
  655.  
  656. satisfied:
  657.     goto loop;
  658. }
  659.  
  660. #endif /* CONFIG_SMP */
  661.  
  662.  
  663. /** Print information about threads & scheduler queues */
  664. void sched_print_list(void)
  665. {
  666.     ipl_t ipl;
  667.     int cpu,i;
  668.     runq_t *r;
  669.     thread_t *t;
  670.     link_t *cur;
  671.  
  672.     /* We are going to mess with scheduler structures,
  673.      * let's not be interrupted */
  674.     ipl = interrupts_disable();
  675.     for (cpu=0;cpu < config.cpu_count; cpu++) {
  676.  
  677.         if (!cpus[cpu].active)
  678.             continue;
  679.  
  680.         spinlock_lock(&cpus[cpu].lock);
  681.         printf("cpu%d: address=%p, nrdy=%ld, needs_relink=%ld\n",
  682.                cpus[cpu].id, &cpus[cpu], atomic_get(&cpus[cpu].nrdy), cpus[cpu].needs_relink);
  683.        
  684.         for (i=0; i<RQ_COUNT; i++) {
  685.             r = &cpus[cpu].rq[i];
  686.             spinlock_lock(&r->lock);
  687.             if (!r->n) {
  688.                 spinlock_unlock(&r->lock);
  689.                 continue;
  690.             }
  691.             printf("\trq[%d]: ", i);
  692.             for (cur=r->rq_head.next; cur!=&r->rq_head; cur=cur->next) {
  693.                 t = list_get_instance(cur, thread_t, rq_link);
  694.                 printf("%d(%s) ", t->tid,
  695.                        thread_states[t->state]);
  696.             }
  697.             printf("\n");
  698.             spinlock_unlock(&r->lock);
  699.         }
  700.         spinlock_unlock(&cpus[cpu].lock);
  701.     }
  702.    
  703.     interrupts_restore(ipl);
  704. }
  705.  
  706. /** @}
  707.  */
  708.