nuttx/sched/sched/sched_mergepending.c

/****************************************************************************
 * sched/sched/sched_mergepending.c
 *
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.  The
 * ASF licenses this file to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance with the
 * License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  See the
 * License for the specific language governing permissions and limitations
 * under the License.
 *
 ****************************************************************************/

/****************************************************************************
 * Included Files
 ****************************************************************************/

#include <nuttx/config.h>

#include <stdbool.h>
#include <sched.h>
#include <queue.h>
#include <assert.h>

#ifdef CONFIG_SMP
#  include <nuttx/spinlock.h>
#endif

#include "irq/irq.h"
#include "sched/sched.h"

/****************************************************************************
 * Pre-processor Definitions
 ****************************************************************************/

#define ALL_CPUS ((cpu_set_t)-1)

/****************************************************************************
 * Public Functions
 ****************************************************************************/

/****************************************************************************
 * Name: nxsched_merge_pending
 *
 * Description:
 *   This function merges the prioritized g_pendingtasks list into the
 *   prioritized ready-to-run task list.
 *
 * Input Parameters:
 *   None
 *
 * Returned Value:
 *   true if the head of the ready-to-run task list has changed indicating
 *     a context switch is needed.
 *
 * Assumptions:
 * - The caller has established a critical section before calling this
 *   function.
 * - The caller handles the condition that occurs if the head of the
 *   ready-to-run task list is changed.
 *
 ****************************************************************************/

#ifndef CONFIG_SMP
bool nxsched_merge_pending(void)
{
  FAR struct tcb_s *ptcb;
  FAR struct tcb_s *pnext;
  FAR struct tcb_s *rtcb;
  FAR struct tcb_s *rprev;
  bool ret = false;

  /* Initialize the inner search loop */

  rtcb = this_task();

  /* Process every TCB in the g_pendingtasks list */

  for (ptcb = (FAR struct tcb_s *)g_pendingtasks.head;
       ptcb;
       ptcb = pnext)
    {
      pnext = ptcb->flink;

      /* REVISIT:  Why don't we just remove the ptcb from pending task list
       * and call nxsched_add_readytorun?
       */

      /* Search the ready-to-run list to find the location to insert the
       * new ptcb. Each is list is maintained in ascending sched_priority
       * order.
       */

      for (;
           (rtcb && ptcb->sched_priority <= rtcb->sched_priority);
           rtcb = rtcb->flink)
        {
        }

      /* Add the ptcb to the spot found in the list.  Check if the
       * ptcb goes at the ends of the ready-to-run list. This would be
       * error condition since the idle test must always be at the end of
       * the ready-to-run list!
       */

      DEBUGASSERT(rtcb);

      /* The ptcb goes just before rtcb */

      rprev = rtcb->blink;
      if (!rprev)
        {
          /* Special case: Inserting ptcb at the head of the list */

          ptcb->flink       = rtcb;
          ptcb->blink       = NULL;
          rtcb->blink       = ptcb;
          g_readytorun.head = (FAR dq_entry_t *)ptcb;
          rtcb->task_state  = TSTATE_TASK_READYTORUN;
          ptcb->task_state  = TSTATE_TASK_RUNNING;
          ret               = true;
        }
      else
        {
          /* Insert in the middle of the list */

          ptcb->flink       = rtcb;
          ptcb->blink       = rprev;
          rprev->flink      = ptcb;
          rtcb->blink       = ptcb;
          ptcb->task_state  = TSTATE_TASK_READYTORUN;
        }

      /* Set up for the next time through */

      rtcb = ptcb;
    }

  /* Mark the input list empty */

  g_pendingtasks.head = NULL;
  g_pendingtasks.tail = NULL;

  return ret;
}
#endif /* !CONFIG_SMP */

/****************************************************************************
 * Name: nxsched_merge_pending
 *
 * Description:
 *   This function merges the prioritized g_pendingtasks list into the
 *   prioritized ready-to-run task list.
 *
 * Input Parameters:
 *   None
 *
 * Returned Value:
 *   true if the head of the ready-to-run task list has changed indicating
 *     a context switch is needed.
 *
 * Assumptions:
 * - The caller has established a critical section before calling this
 *   function.
 * - The caller handles the condition that occurs if the head of the
 *   ready-to-run task list is changed.
 *
 ****************************************************************************/

#ifdef CONFIG_SMP
bool nxsched_merge_pending(void)
{
  FAR struct tcb_s *rtcb;
  FAR struct tcb_s *ptcb;
  FAR struct tcb_s *tcb;
  bool ret = false;
  int cpu;
  int me;

  /* Remove and process every TCB in the g_pendingtasks list.
   *
   * Do nothing if (1) pre-emption is still disabled (by any CPU), or (2) if
   * some CPU other than this one is in a critical section.
   */

  me = this_cpu();
  if (!nxsched_islocked_global() && !irq_cpu_locked(me))
    {
      /* Find the CPU that is executing the lowest priority task */

      ptcb = (FAR struct tcb_s *)dq_peek((FAR dq_queue_t *)&g_pendingtasks);
      if (ptcb == NULL)
        {
          /* The pending task list is empty */

          goto errout;
        }

      cpu  = nxsched_select_cpu(ALL_CPUS); /* REVISIT:  Maybe ptcb->affinity */
      rtcb = current_task(cpu);

      /* Loop while there is a higher priority task in the pending task list
       * than in the lowest executing task.
       *
       * Normally, this loop should execute no more than CONFIG_SMP_NCPUS
       * times.  That number could be larger, however, if the CPU affinity
       * sets do not include all CPUs. In that case, the excess TCBs will
       * end up in the g_readytorun list.
       */

      while (ptcb->sched_priority > rtcb->sched_priority)
        {
          /* Remove the task from the pending task list */

          tcb = (FAR struct tcb_s *)
            dq_remfirst((FAR dq_queue_t *)&g_pendingtasks);

          /* Add the pending task to the correct ready-to-run list. */

          ret |= nxsched_add_readytorun(tcb);

          /* This operation could cause the scheduler to become locked.
           * Check if that happened.
           */

          if (nxsched_islocked_global() || irq_cpu_locked(me))
            {
              /* Yes.. then we may have incorrectly placed some TCBs in the
               * g_readytorun list (unlikely, but possible).  We will have to
               * move them back to the pending task list.
               */

              nxsched_merge_prioritized((FAR dq_queue_t *)&g_readytorun,
                                        (FAR dq_queue_t *)&g_pendingtasks,
                                        TSTATE_TASK_PENDING);

              /* And return with the scheduler locked and tasks in the
               * pending task list.
               */

              goto errout;
            }

          /* Set up for the next time through the loop */

          ptcb = (FAR struct tcb_s *)
            dq_peek((FAR dq_queue_t *)&g_pendingtasks);
          if (ptcb == NULL)
            {
              /* The pending task list is empty */

              goto errout;
            }

          cpu  = nxsched_select_cpu(ALL_CPUS); /* REVISIT:  Maybe ptcb->affinity */
          rtcb = current_task(cpu);
        }

      /* No more pending tasks can be made running.  Move any remaining
       * tasks in the pending task list to the ready-to-run task list.
       */

      nxsched_merge_prioritized((FAR dq_queue_t *)&g_pendingtasks,
                                (FAR dq_queue_t *)&g_readytorun,
                                TSTATE_TASK_READYTORUN);
    }

errout:

  return ret;
}
#endif /* CONFIG_SMP */