336 lines
11 KiB
C
336 lines
11 KiB
C
/****************************************************************************
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* sched/sched_removereadytorun.c
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*
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* Copyright (C) 2007-2009, 2012, 2016-2017 Gregory Nutt. All rights reserved.
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* Author: Gregory Nutt <gnutt@nuttx.org>
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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*
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in
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* the documentation and/or other materials provided with the
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* distribution.
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* 3. Neither the name NuttX nor the names of its contributors may be
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* used to endorse or promote products derived from this software
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* without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
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* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
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* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
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* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
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* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
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* OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
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* AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
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* ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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* POSSIBILITY OF SUCH DAMAGE.
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*
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****************************************************************************/
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/****************************************************************************
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* Included Files
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****************************************************************************/
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#include <nuttx/config.h>
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#include <stdbool.h>
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#include <queue.h>
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#include <assert.h>
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#include "irq/irq.h"
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#include "sched/sched.h"
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/****************************************************************************
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* Public Functions
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****************************************************************************/
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/****************************************************************************
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* Name: sched_removereadytorun
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*
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* Description:
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* This function removes a TCB from the ready to run list.
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*
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* Inputs:
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* rtcb - Points to the TCB that is ready-to-run
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*
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* Return Value:
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* true if the currently active task (the head of the ready-to-run list)
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* has changed.
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*
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* Assumptions:
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* - The caller has established a critical section before calling this
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* function (calling sched_lock() first is NOT a good idea -- use
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* enter_critical_section()).
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* - The caller handles the condition that occurs if the head of the
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* ready-to-run list is changed.
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*
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****************************************************************************/
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#ifndef CONFIG_SMP
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bool sched_removereadytorun(FAR struct tcb_s *rtcb)
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{
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bool doswitch = false;
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/* Check if the TCB to be removed is at the head of the ready to run list.
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* There is only one list, g_readytorun, and it always contains the
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* currently running task. If we are removing the head of this list,
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* then we are removing the currently active task.
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*/
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if (rtcb->blink == NULL)
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{
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/* There must always be at least one task in the list (the IDLE task)
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* after the TCB being removed.
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*/
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FAR struct tcb_s *nxttcb = (FAR struct tcb_s *)rtcb->flink;
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DEBUGASSERT(nxttcb != NULL);
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nxttcb->task_state = TSTATE_TASK_RUNNING;
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doswitch = true;
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}
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/* Remove the TCB from the ready-to-run list. In the non-SMP case, this
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* is always the g_readytorun list.
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*/
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dq_rem((FAR dq_entry_t *)rtcb, (FAR dq_queue_t *)&g_readytorun);
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/* Since the TCB is not in any list, it is now invalid */
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rtcb->task_state = TSTATE_TASK_INVALID;
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return doswitch;
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}
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#endif /* !CONFIG_SMP */
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/****************************************************************************
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* Name: sched_removereadytorun
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*
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* Description:
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* This function removes a TCB from the ready to run list.
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*
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* Inputs:
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* rtcb - Points to the TCB that is ready-to-run
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*
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* Return Value:
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* true if the currently active task (the head of the ready-to-run list)
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* has changed.
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*
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* Assumptions:
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* - The caller has established a critical section before calling this
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* function (calling sched_lock() first is NOT a good idea -- use
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* enter_critical_section()).
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* - The caller handles the condition that occurs if the head of the
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* ready-to-run list is changed.
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*
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****************************************************************************/
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#ifdef CONFIG_SMP
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bool sched_removereadytorun(FAR struct tcb_s *rtcb)
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{
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FAR dq_queue_t *tasklist;
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bool doswitch = false;
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int cpu;
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/* Which CPU (if any) is the task running on? Which task list holds the
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* TCB?
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*/
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cpu = rtcb->cpu;
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tasklist = TLIST_HEAD(rtcb->task_state, cpu);
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/* Check if the TCB to be removed is at the head of a ready-to-run list.
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* For the case of SMP, there are two lists involved: (1) the
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* g_readytorun list that holds non-running tasks that have not been
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* assigned to a CPU, and (2) and the g_assignedtasks[] lists which hold
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* tasks assigned a CPU, including the task that is currently running on
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* that CPU. Only this latter list contains the currently active task
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* only only removing the head of that list can result in a context
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* switch.
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*
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* rtcb->blink == NULL will tell us if the TCB is at the head of the
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* ready-to-run list and, hence, a candidate for the new running task.
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*
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* If so, then the tasklist RUNNABLE attribute will inform us if the list
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* holds the currently executing task and, hence, if a context switch
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* should occur.
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*/
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if (rtcb->blink == NULL && TLIST_ISRUNNABLE(rtcb->task_state))
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{
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FAR struct tcb_s *nxttcb;
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FAR struct tcb_s *rtrtcb = NULL;
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int me;
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/* There must always be at least one task in the list (the IDLE task)
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* after the TCB being removed.
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*/
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nxttcb = (FAR struct tcb_s *)rtcb->flink;
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DEBUGASSERT(nxttcb != NULL);
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/* If we are modifying the head of some assigned task list other than
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* our own, we will need to stop that CPU.
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*/
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me = this_cpu();
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if (cpu != me)
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{
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DEBUGVERIFY(up_cpu_pause(cpu));
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}
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/* The task is running but the CPU that it was running on has been
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* paused. We can now safely remove its TCB from the ready-to-run
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* task list. In the SMP case this may be either the g_readytorun()
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* or the g_assignedtasks[cpu] list.
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*/
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dq_rem((FAR dq_entry_t *)rtcb, tasklist);
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/* Which task will go at the head of the list? It will be either the
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* next tcb in the assigned task list (nxttcb) or a TCB in the
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* g_readytorun list. We can only select a task from that list if
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* the affinity mask includes the current CPU.
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*
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* If pre-emption is locked or another CPU is in a critical section,
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* then use the 'nxttcb' which will probably be the IDLE thread.
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* REVISIT: What if it is not the IDLE thread?
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*/
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if (!spin_islocked(&g_cpu_schedlock) && !irq_cpu_locked(me))
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{
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/* Search for the highest priority task that can run on this
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* CPU.
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*/
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for (rtrtcb = (FAR struct tcb_s *)g_readytorun.head;
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rtrtcb != NULL && !CPU_ISSET(cpu, &rtrtcb->affinity);
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rtrtcb = (FAR struct tcb_s *)rtrtcb->flink);
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}
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/* Did we find a task in the g_readytorun list? Which task should
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* we use? We decide strictly by the priority of the two tasks:
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* Either (1) the task currently at the head of the g_assignedtasks[cpu]
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* list (nexttcb) or (2) the highest priority task from the
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* g_readytorun list with matching affinity (rtrtcb).
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*/
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if (rtrtcb != NULL && rtrtcb->sched_priority >= nxttcb->sched_priority)
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{
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FAR struct tcb_s *tmptcb;
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/* The TCB at the head of the ready to run list has the higher
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* priority. Remove that task from the head of the g_readytorun
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* list and add to the head of the g_assignedtasks[cpu] list.
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*/
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tmptcb = (FAR struct tcb_s *)
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dq_remfirst((FAR dq_queue_t *)&g_readytorun);
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DEBUGASSERT(tmptcb == rtrtcb);
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dq_addfirst((FAR dq_entry_t *)tmptcb, tasklist);
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tmptcb->cpu = cpu;
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nxttcb = tmptcb;
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}
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/* Will pre-emption be disabled after the switch? If the lockcount is
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* greater than zero, then this task/this CPU holds the scheduler lock.
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*/
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if (nxttcb->lockcount > 0)
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{
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/* Yes... make sure that scheduling logic knows about this */
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spin_setbit(&g_cpu_lockset, cpu, &g_cpu_locksetlock,
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&g_cpu_schedlock);
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}
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else
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{
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/* No.. we may need to perform release our hold on the lock. */
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spin_clrbit(&g_cpu_lockset, cpu, &g_cpu_locksetlock,
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&g_cpu_schedlock);
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}
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/* Adjust global IRQ controls. If irqcount is greater than zero,
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* then this task/this CPU holds the IRQ lock
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*/
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if (nxttcb->irqcount > 0)
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{
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/* Yes... make sure that scheduling logic on other CPUs knows
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* that we hold the IRQ lock.
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*/
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spin_setbit(&g_cpu_irqset, cpu, &g_cpu_irqsetlock,
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&g_cpu_irqlock);
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}
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/* No.. This CPU will be relinquishing the lock. But this works
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* differently if we are performing a context switch from an
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* interrupt handler and the interrupt handler has established
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* a critical section. We can detect this case when
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* g_cpu_nestcount[me] > 0.
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*/
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else if (g_cpu_nestcount[me] <= 0)
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{
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/* Release our hold on the IRQ lock. */
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spin_clrbit(&g_cpu_irqset, cpu, &g_cpu_irqsetlock,
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&g_cpu_irqlock);
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}
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/* Sanity check. g_cpu_netcount should be greater than zero
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* only while we are within the critical section and within
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* an interrupt handler. If we are not in an interrupt handler
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* then there is a problem; perhaps some logic previously
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* called enter_critical_section() with no matching call to
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* leave_critical_section(), leaving the non-zero count.
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*/
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else
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{
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DEBUGASSERT(up_interrupt_context());
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}
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nxttcb->task_state = TSTATE_TASK_RUNNING;
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/* All done, restart the other CPU (if it was paused). */
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doswitch = true;
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if (cpu != me)
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{
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/* In this we will not want to report a context switch to this
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* CPU. Only the other CPU is affected.
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*/
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DEBUGVERIFY(up_cpu_resume(cpu));
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doswitch = false;
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}
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}
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else
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{
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/* The task is not running. Just remove its TCB from the ready-to-run
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* list. In the SMP case this may be either the g_readytorun() or the
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* g_assignedtasks[cpu] list.
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*/
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dq_rem((FAR dq_entry_t *)rtcb, tasklist);
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}
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/* Since the TCB is no longer in any list, it is now invalid */
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rtcb->task_state = TSTATE_TASK_INVALID;
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return doswitch;
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}
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#endif /* CONFIG_SMP */
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