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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. #include <proc/scheduler.h>
  30. #include <proc/thread.h>
  31. #include <proc/task.h>
  32. #include <cpu.h>
  33. #include <mm/vm.h>
  34. #include <config.h>
  35. #include <context.h>
  36. #include <func.h>
  37. #include <arch.h>
  38. #include <arch/asm.h>
  39. #include <list.h>
  40. #include <panic.h>
  41. #include <typedefs.h>
  42. #include <mm/page.h>
  43. #include <synch/spinlock.h>
  44. #include <arch/faddr.h>
  45. #include <arch/atomic.h>
  46.  
  47. volatile int nrdy;
  48.  
  49.  
  50. /** Initialize context switching
  51.  *
  52.  * Initialize context switching and lazy FPU
  53.  * context switching.
  54.  *
  55.  */
  56. void before_thread_runs(void)
  57. {
  58.     before_thread_runs_arch();
  59.     fpu_context_restore(&(THREAD->saved_fpu_context));
  60. }
  61.  
  62.  
  63. /** Initialize scheduler
  64.  *
  65.  * Initialize kernel scheduler.
  66.  *
  67.  */
  68. void scheduler_init(void)
  69. {
  70. }
  71.  
  72.  
  73. /** Get thread to be scheduled
  74.  *
  75.  * Get the optimal thread to be scheduled
  76.  * according to thread accounting and scheduler
  77.  * policy.
  78.  *
  79.  * @return Thread to be scheduled.
  80.  *
  81.  */
  82. struct thread *find_best_thread(void)
  83. {
  84.     thread_t *t;
  85.     runq_t *r;
  86.     int i, n;
  87.  
  88. loop:
  89.     cpu_priority_high();
  90.  
  91.     spinlock_lock(&CPU->lock);
  92.     n = CPU->nrdy;
  93.     spinlock_unlock(&CPU->lock);
  94.  
  95.     cpu_priority_low();
  96.    
  97.     if (n == 0) {
  98.         #ifdef __SMP__
  99.         /*
  100.          * If the load balancing thread is not running, wake it up and
  101.          * set CPU-private flag that the kcpulb has been started.
  102.          */
  103.         if (test_and_set(&CPU->kcpulbstarted) == 0) {
  104.                 waitq_wakeup(&CPU->kcpulb_wq, 0);
  105.             goto loop;
  106.         }
  107.         #endif /* __SMP__ */
  108.        
  109.         /*
  110.          * For there was nothing to run, the CPU goes to sleep
  111.          * until a hardware interrupt or an IPI comes.
  112.          * This improves energy saving and hyperthreading.
  113.          * On the other hand, several hardware interrupts can be ignored.
  114.          */
  115.          cpu_sleep();
  116.          goto loop;
  117.     }
  118.  
  119.     cpu_priority_high();
  120.  
  121.     for (i = 0; i<RQ_COUNT; i++) {
  122.         r = &CPU->rq[i];
  123.         spinlock_lock(&r->lock);
  124.         if (r->n == 0) {
  125.             /*
  126.              * If this queue is empty, try a lower-priority queue.
  127.              */
  128.             spinlock_unlock(&r->lock);
  129.             continue;
  130.         }
  131.    
  132.         atomic_dec(&nrdy);
  133.  
  134.         spinlock_lock(&CPU->lock);
  135.         CPU->nrdy--;
  136.         spinlock_unlock(&CPU->lock);
  137.  
  138.         r->n--;
  139.  
  140.         /*
  141.          * Take the first thread from the queue.
  142.          */
  143.         t = list_get_instance(r->rq_head.next, thread_t, rq_link);
  144.         list_remove(&t->rq_link);
  145.  
  146.         spinlock_unlock(&r->lock);
  147.  
  148.         spinlock_lock(&t->lock);
  149.         t->cpu = CPU;
  150.  
  151.         t->ticks = us2ticks((i+1)*10000);
  152.         t->pri = i; /* eventually correct rq index */
  153.  
  154.         /*
  155.          * Clear the X_STOLEN flag so that t can be migrated when load balancing needs emerge.
  156.          */
  157.         t->flags &= ~X_STOLEN;
  158.         spinlock_unlock(&t->lock);
  159.  
  160.         return t;
  161.     }
  162.     goto loop;
  163.  
  164. }
  165.  
  166.  
  167. /** Prevent rq starvation
  168.  *
  169.  * Prevent low priority threads from starving in rq's.
  170.  *
  171.  * When the function decides to relink rq's, it reconnects
  172.  * respective pointers so that in result threads with 'pri'
  173.  * greater or equal 'start' are moved to a higher-priority queue.
  174.  *
  175.  * @param start Threshold priority.
  176.  *
  177.  */
  178. void relink_rq(int start)
  179. {
  180.     link_t head;
  181.     runq_t *r;
  182.     int i, n;
  183.  
  184.     list_initialize(&head);
  185.     spinlock_lock(&CPU->lock);
  186.     if (CPU->needs_relink > NEEDS_RELINK_MAX) {
  187.         for (i = start; i<RQ_COUNT-1; i++) {
  188.             /* remember and empty rq[i + 1] */
  189.             r = &CPU->rq[i + 1];
  190.             spinlock_lock(&r->lock);
  191.             list_concat(&head, &r->rq_head);
  192.             n = r->n;
  193.             r->n = 0;
  194.             spinlock_unlock(&r->lock);
  195.        
  196.             /* append rq[i + 1] to rq[i] */
  197.             r = &CPU->rq[i];
  198.             spinlock_lock(&r->lock);
  199.             list_concat(&r->rq_head, &head);
  200.             r->n += n;
  201.             spinlock_unlock(&r->lock);
  202.         }
  203.         CPU->needs_relink = 0;
  204.     }
  205.     spinlock_unlock(&CPU->lock);               
  206.  
  207. }
  208.  
  209.  
  210. /** The scheduler
  211.  *
  212.  * The thread scheduling procedure.
  213.  *
  214.  */
  215. void scheduler(void)
  216. {
  217.     volatile pri_t pri;
  218.  
  219.     pri = cpu_priority_high();
  220.  
  221.     if (haltstate)
  222.         halt();
  223.  
  224.     if (THREAD) {
  225.         spinlock_lock(&THREAD->lock);
  226.         fpu_context_save(&(THREAD->saved_fpu_context));
  227.         if (!context_save(&THREAD->saved_context)) {
  228.             /*
  229.              * This is the place where threads leave scheduler();
  230.              */
  231.             before_thread_runs();
  232.                 spinlock_unlock(&THREAD->lock);
  233.             cpu_priority_restore(THREAD->saved_context.pri);
  234.             return;
  235.         }
  236.         THREAD->saved_context.pri = pri;
  237.     }
  238.  
  239.     /*
  240.      * We may not keep the old stack.
  241.      * Reason: If we kept the old stack and got blocked, for instance, in
  242.      * find_best_thread(), the old thread could get rescheduled by another
  243.      * CPU and overwrite the part of its own stack that was also used by
  244.      * the scheduler on this CPU.
  245.      *
  246.      * Moreover, we have to bypass the compiler-generated POP sequence
  247.      * which is fooled by SP being set to the very top of the stack.
  248.      * Therefore the scheduler() function continues in
  249.      * scheduler_separated_stack().
  250.      */
  251.     context_save(&CPU->saved_context);
  252.     context_set(&CPU->saved_context, FADDR(scheduler_separated_stack), CPU->stack, CPU_STACK_SIZE);
  253.     context_restore(&CPU->saved_context);
  254.     /* not reached */
  255. }
  256.  
  257.  
  258. /** Scheduler stack switch wrapper
  259.  *
  260.  * Second part of the scheduler() function
  261.  * using new stack. Handling the actual context
  262.  * switch to a new thread.
  263.  *
  264.  */
  265. void scheduler_separated_stack(void)
  266. {
  267.     int priority;
  268.  
  269.     if (THREAD) {
  270.         switch (THREAD->state) {
  271.             case Running:
  272.                 THREAD->state = Ready;
  273.                 spinlock_unlock(&THREAD->lock);
  274.                 thread_ready(THREAD);
  275.                 break;
  276.  
  277.             case Exiting:
  278.                 frame_free((__address) THREAD->kstack);
  279.                 if (THREAD->ustack) {
  280.                     frame_free((__address) THREAD->ustack);
  281.                 }
  282.                
  283.                 /*
  284.                  * Detach from the containing task.
  285.                  */
  286.                 spinlock_lock(&TASK->lock);
  287.                 list_remove(&THREAD->th_link);
  288.                 spinlock_unlock(&TASK->lock);
  289.  
  290.                 spinlock_unlock(&THREAD->lock);
  291.                
  292.                 spinlock_lock(&threads_lock);
  293.                 list_remove(&THREAD->threads_link);
  294.                 spinlock_unlock(&threads_lock);
  295.  
  296.                 spinlock_lock(&CPU->lock);
  297.                 if(CPU->fpu_owner==THREAD) CPU->fpu_owner=NULL;
  298.                 spinlock_unlock(&CPU->lock);
  299.  
  300.                
  301.                 free(THREAD);
  302.                
  303.                 break;
  304.                
  305.             case Sleeping:
  306.                 /*
  307.                  * Prefer the thread after it's woken up.
  308.                  */
  309.                 THREAD->pri = -1;
  310.  
  311.                 /*
  312.                  * We need to release wq->lock which we locked in waitq_sleep().
  313.                  * Address of wq->lock is kept in THREAD->sleep_queue.
  314.                  */
  315.                 spinlock_unlock(&THREAD->sleep_queue->lock);
  316.  
  317.                 /*
  318.                  * Check for possible requests for out-of-context invocation.
  319.                  */
  320.                 if (THREAD->call_me) {
  321.                     THREAD->call_me(THREAD->call_me_with);
  322.                     THREAD->call_me = NULL;
  323.                     THREAD->call_me_with = NULL;
  324.                 }
  325.  
  326.                 spinlock_unlock(&THREAD->lock);
  327.                
  328.                 break;
  329.  
  330.             default:
  331.                 /*
  332.                  * Entering state is unexpected.
  333.                  */
  334.                 panic("tid%d: unexpected state %s\n", THREAD->tid, thread_states[THREAD->state]);
  335.                 break;
  336.         }
  337.         THREAD = NULL;
  338.     }
  339.    
  340.     THREAD = find_best_thread();
  341.    
  342.     spinlock_lock(&THREAD->lock);
  343.     priority = THREAD->pri;
  344.     spinlock_unlock(&THREAD->lock);
  345.    
  346.     relink_rq(priority);       
  347.  
  348.     spinlock_lock(&THREAD->lock);  
  349.  
  350.     /*
  351.      * If both the old and the new task are the same, lots of work is avoided.
  352.      */
  353.     if (TASK != THREAD->task) {
  354.         vm_t *m1 = NULL;
  355.         vm_t *m2;
  356.  
  357.         if (TASK) {
  358.             spinlock_lock(&TASK->lock);
  359.             m1 = TASK->vm;
  360.             spinlock_unlock(&TASK->lock);
  361.         }
  362.  
  363.         spinlock_lock(&THREAD->task->lock);
  364.         m2 = THREAD->task->vm;
  365.         spinlock_unlock(&THREAD->task->lock);
  366.        
  367.         /*
  368.          * Note that it is possible for two tasks to share one vm mapping.
  369.          */
  370.         if (m1 != m2) {
  371.             /*
  372.              * Both tasks and vm mappings are different.
  373.              * Replace the old one with the new one.
  374.              */
  375.             if (m1) {
  376.                 vm_uninstall(m1);
  377.             }
  378.             vm_install(m2);
  379.         }
  380.         TASK = THREAD->task;   
  381.     }
  382.  
  383.     THREAD->state = Running;
  384.  
  385.     #ifdef SCHEDULER_VERBOSE
  386.     printf("cpu%d: tid %d (pri=%d,ticks=%d,nrdy=%d)\n", CPU->id, THREAD->tid, THREAD->pri, THREAD->ticks, CPU->nrdy);
  387.     #endif 
  388.  
  389.     context_restore(&THREAD->saved_context);
  390.     /* not reached */
  391. }
  392.  
  393.  
  394. #ifdef __SMP__
  395. /** Load balancing thread
  396.  *
  397.  * SMP load balancing thread, supervising thread supplies
  398.  * for the CPU it's wired to.
  399.  *
  400.  * @param arg Generic thread argument (unused).
  401.  *
  402.  */
  403. void kcpulb(void *arg)
  404. {
  405.     thread_t *t;
  406.     int count, i, j, k = 0;
  407.     pri_t pri;
  408.  
  409. loop:
  410.     /*
  411.      * Sleep until there's some work to do.
  412.      */
  413.     waitq_sleep(&CPU->kcpulb_wq);
  414.  
  415. not_satisfied:
  416.     /*
  417.      * Calculate the number of threads that will be migrated/stolen from
  418.      * other CPU's. Note that situation can have changed between two
  419.      * passes. Each time get the most up to date counts.
  420.      */
  421.     pri = cpu_priority_high();
  422.     spinlock_lock(&CPU->lock);
  423.     count = nrdy / config.cpu_active;
  424.     count -= CPU->nrdy;
  425.     spinlock_unlock(&CPU->lock);
  426.     cpu_priority_restore(pri);
  427.  
  428.     if (count <= 0)
  429.         goto satisfied;
  430.  
  431.     /*
  432.      * Searching least priority queues on all CPU's first and most priority queues on all CPU's last.
  433.      */
  434.     for (j=RQ_COUNT-1; j >= 0; j--) {
  435.         for (i=0; i < config.cpu_active; i++) {
  436.             link_t *l;
  437.             runq_t *r;
  438.             cpu_t *cpu;
  439.  
  440.             cpu = &cpus[(i + k) % config.cpu_active];
  441.             r = &cpu->rq[j];
  442.  
  443.             /*
  444.              * Not interested in ourselves.
  445.              * Doesn't require interrupt disabling for kcpulb is X_WIRED.
  446.              */
  447.             if (CPU == cpu)
  448.                 continue;
  449.  
  450. restart:        pri = cpu_priority_high();
  451.             spinlock_lock(&r->lock);
  452.             if (r->n == 0) {
  453.                 spinlock_unlock(&r->lock);
  454.                 cpu_priority_restore(pri);
  455.                 continue;
  456.             }
  457.        
  458.             t = NULL;
  459.             l = r->rq_head.prev;    /* search rq from the back */
  460.             while (l != &r->rq_head) {
  461.                 t = list_get_instance(l, thread_t, rq_link);
  462.                 /*
  463.                      * We don't want to steal CPU-wired threads neither threads already stolen.
  464.                  * The latter prevents threads from migrating between CPU's without ever being run.
  465.                      * We don't want to steal threads whose FPU context is still in CPU
  466.                  */
  467.                 spinlock_lock(&t->lock);
  468.                 if ( (!(t->flags & (X_WIRED | X_STOLEN))) && (!(t->fpu_context_engaged)) ) {
  469.                     /*
  470.                      * Remove t from r.
  471.                      */
  472.  
  473.                     spinlock_unlock(&t->lock);
  474.                    
  475.                     /*
  476.                      * Here we have to avoid deadlock with relink_rq(),
  477.                      * because it locks cpu and r in a different order than we do.
  478.                      */
  479.                     if (!spinlock_trylock(&cpu->lock)) {
  480.                         /* Release all locks and try again. */
  481.                         spinlock_unlock(&r->lock);
  482.                         cpu_priority_restore(pri);
  483.                         goto restart;
  484.                     }
  485.                     cpu->nrdy--;
  486.                     spinlock_unlock(&cpu->lock);
  487.  
  488.                     atomic_dec(&nrdy);
  489.  
  490.                         r->n--;
  491.                     list_remove(&t->rq_link);
  492.  
  493.                     break;
  494.                 }
  495.                 spinlock_unlock(&t->lock);
  496.                 l = l->prev;
  497.                 t = NULL;
  498.             }
  499.             spinlock_unlock(&r->lock);
  500.  
  501.             if (t) {
  502.                 /*
  503.                  * Ready t on local CPU
  504.                  */
  505.                 spinlock_lock(&t->lock);
  506.                 #ifdef KCPULB_VERBOSE
  507.                 printf("kcpulb%d: TID %d -> cpu%d, nrdy=%d, avg=%d\n", CPU->id, t->tid, CPU->id, CPU->nrdy, nrdy / config.cpu_active);
  508.                 #endif
  509.                 t->flags |= X_STOLEN;
  510.                 spinlock_unlock(&t->lock);
  511.    
  512.                 thread_ready(t);
  513.  
  514.                 cpu_priority_restore(pri);
  515.    
  516.                 if (--count == 0)
  517.                     goto satisfied;
  518.                    
  519.                 /*
  520.                              * We are not satisfied yet, focus on another CPU next time.
  521.                  */
  522.                 k++;
  523.                
  524.                 continue;
  525.             }
  526.             cpu_priority_restore(pri);
  527.         }
  528.     }
  529.  
  530.     if (CPU->nrdy) {
  531.         /*
  532.          * Be a little bit light-weight and let migrated threads run.
  533.          */
  534.         scheduler();
  535.     }
  536.     else {
  537.         /*
  538.          * We failed to migrate a single thread.
  539.          * Something more sophisticated should be done.
  540.          */
  541.         scheduler();
  542.     }
  543.        
  544.     goto not_satisfied;
  545.    
  546. satisfied:
  547.     /*
  548.      * Tell find_best_thread() to wake us up later again.
  549.      */
  550.     CPU->kcpulbstarted = 0;
  551.     goto loop;
  552. }
  553.  
  554. #endif /* __SMP__ */
  555.