nuttx/sched/sched/sched_removereadytorun.c

/****************************************************************************
 * sched/sched/sched_removereadytorun.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 <assert.h>

#include <nuttx/queue.h>
#include <nuttx/sched_note.h>

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

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

/****************************************************************************
 * Name: nxsched_remove_readytorun
 *
 * Description:
 *   This function removes a TCB from the ready to run list.
 *
 * Input Parameters:
 *   rtcb - Points to the TCB that is ready-to-run
 *   merge - Merge pending list or not
 *
 * Returned Value:
 *   true if the currently active task (the head of the ready-to-run list)
 *     has changed.
 *
 * Assumptions:
 * - The caller has established a critical section before calling this
 *   function (calling sched_lock() first is NOT a good idea -- use
 *   enter_critical_section()).
 * - The caller handles the condition that occurs if the head of the
 *   ready-to-run list is changed.
 *
 ****************************************************************************/

#ifndef CONFIG_SMP
bool nxsched_remove_readytorun(FAR struct tcb_s *rtcb, bool merge)
{
  FAR dq_queue_t *tasklist;
  bool doswitch = false;

  tasklist = TLIST_HEAD(rtcb);

  /* Check if the TCB to be removed is at the head of the ready to run list.
   * There is only one list, g_readytorun, and it always contains the
   * currently running task.  If we are removing the head of this list,
   * then we are removing the currently active task.
   */

  if (rtcb->blink == NULL && TLIST_ISRUNNABLE(rtcb->task_state))
    {
      /* There must always be at least one task in the list (the IDLE task)
       * after the TCB being removed.
       */

      FAR struct tcb_s *nxttcb = (FAR struct tcb_s *)rtcb->flink;
      DEBUGASSERT(nxttcb != NULL);

      nxttcb->task_state = TSTATE_TASK_RUNNING;
      doswitch = true;
    }

  /* Remove the TCB from the ready-to-run list.  In the non-SMP case, this
   * is always the g_readytorun list.
   */

  dq_rem((FAR dq_entry_t *)rtcb, tasklist);

  /* Since the TCB is not in any list, it is now invalid */

  rtcb->task_state = TSTATE_TASK_INVALID;

  if (list_pendingtasks()->head && merge)
    {
      doswitch |= nxsched_merge_pending();
    }

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

/****************************************************************************
 * Name: nxsched_remove_readytorun
 *
 * Description:
 *   This function removes a TCB from the ready to run list.
 *
 * Input Parameters:
 *   rtcb - Points to the TCB that is ready-to-run
 *   merge - Merge pending list or not
 *
 * Returned Value:
 *   true if the currently active task (the head of the ready-to-run list)
 *     has changed.
 *
 * Assumptions:
 * - The caller has established a critical section before calling this
 *   function (calling sched_lock() first is NOT a good idea -- use
 *   enter_critical_section()).
 * - The caller handles the condition that occurs if the head of the
 *   ready-to-run list is changed.
 *
 ****************************************************************************/

#ifdef CONFIG_SMP
bool nxsched_remove_readytorun(FAR struct tcb_s *rtcb, bool merge)
{
  FAR dq_queue_t *tasklist;
  bool doswitch = false;
  int cpu;

  /* Which CPU (if any) is the task running on?  Which task list holds the
   * TCB?
   */

  cpu      = rtcb->cpu;
  tasklist = TLIST_HEAD(rtcb, cpu);

  /* Check if the TCB to be removed is at the head of a ready-to-run list.
   * For the case of SMP, there are two lists involved:  (1) the
   * g_readytorun list that holds non-running tasks that have not been
   * assigned to a CPU, and (2) and the g_assignedtasks[] lists which hold
   * tasks assigned a CPU, including the task that is currently running on
   * that CPU.  Only this latter list contains the currently active task
   * only removing the head of that list can result in a context switch.
   *
   * rtcb->blink == NULL will tell us if the TCB is at the head of the
   * ready-to-run list and, hence, a candidate for the new running task.
   *
   * If so, then the tasklist RUNNABLE attribute will inform us if the list
   * holds the currently executing task and, hence, if a context switch
   * should occur.
   */

  if (rtcb->blink == NULL && TLIST_ISRUNNABLE(rtcb->task_state))
    {
      FAR struct tcb_s *nxttcb;
      FAR struct tcb_s *rtrtcb = NULL;
      int me;

      /* There must always be at least one task in the list (the IDLE task)
       * after the TCB being removed.
       */

      nxttcb = rtcb->flink;
      DEBUGASSERT(nxttcb != NULL);

      /* If we are modifying the head of some assigned task list other than
       * our own, we will need to stop that CPU.
       */

      me = this_cpu();
      if (cpu != me)
        {
          DEBUGVERIFY(up_cpu_pause(cpu));
        }

      /* The task is running but the CPU that it was running on has been
       * paused.  We can now safely remove its TCB from the ready-to-run
       * task list.  In the SMP case this may be either the g_readytorun()
       * or the g_assignedtasks[cpu] list.
       */

      dq_rem((FAR dq_entry_t *)rtcb, tasklist);

      /* Which task will go at the head of the list?  It will be either the
       * next tcb in the assigned task list (nxttcb) or a TCB in the
       * g_readytorun list.  We can only select a task from that list if
       * the affinity mask includes the current CPU.
       */

      /* Search for the highest priority task that can run on this
       * CPU.
       */

      for (rtrtcb = (FAR struct tcb_s *)list_readytorun()->head;
           rtrtcb != NULL && !CPU_ISSET(cpu, &rtrtcb->affinity);
           rtrtcb = rtrtcb->flink);

      /* Did we find a task in the g_readytorun list?  Which task should
       * we use?  We decide strictly by the priority of the two tasks:
       * Either (1) the task currently at the head of the
       * g_assignedtasks[cpu] list (nexttcb) or (2) the highest priority
       * task from the g_readytorun list with matching affinity (rtrtcb).
       */

      if (rtrtcb != NULL && rtrtcb->sched_priority >= nxttcb->sched_priority)
        {
          /* The TCB rtrtcb has the higher priority and it can be run on
           * target CPU. Remove that task (rtrtcb) from the g_readytorun
           * list and add to the head of the g_assignedtasks[cpu] list.
           */

          dq_rem((FAR dq_entry_t *)rtrtcb, list_readytorun());
          dq_addfirst((FAR dq_entry_t *)rtrtcb, tasklist);

          rtrtcb->cpu = cpu;
          nxttcb = rtrtcb;
        }

      /* Will pre-emption be disabled after the switch?  If the lockcount is
       * greater than zero, then this task/this CPU holds the scheduler lock.
       */

      if (nxttcb->lockcount > 0)
        {
          /* Yes... make sure that scheduling logic knows about this */

          g_cpu_lockset |= (1 << cpu);
        }
      else
        {
          /* No.. we may need to perform release our hold on the lock. */

          g_cpu_lockset &= ~(1 << cpu);
        }

      /* NOTE: If the task runs on another CPU(cpu), adjusting global IRQ
       * controls will be done in the pause handler on the new CPU(cpu).
       * If the task is scheduled on this CPU(me), do nothing because
       * this CPU already has a critical section
       */

      nxttcb->task_state = TSTATE_TASK_RUNNING;

      /* All done, restart the other CPU (if it was paused). */

      doswitch = true;
      if (cpu != me)
        {
          /* In this we will not want to report a context switch to this
           * CPU.  Only the other CPU is affected.
           */

          DEBUGVERIFY(up_cpu_resume(cpu));
          doswitch = false;
        }
    }
  else
    {
      /* The task is not running.  Just remove its TCB from the ready-to-run
       * list.  In the SMP case this may be either the g_readytorun() or the
       * g_assignedtasks[cpu] list.
       */

      dq_rem((FAR dq_entry_t *)rtcb, tasklist);
    }

  /* Since the TCB is no longer in any list, it is now invalid */

  rtcb->task_state = TSTATE_TASK_INVALID;

  if (list_pendingtasks()->head && merge)
    {
      doswitch |= nxsched_merge_pending();
    }

  return doswitch;
}
#endif /* CONFIG_SMP */