127 lines
4.2 KiB
C
127 lines
4.2 KiB
C
/****************************************************************************
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* sched/sched/sched_cpuselect.c
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*
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* Copyright (C) 2016 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 <sys/types.h>
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#include <assert.h>
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#include <nuttx/sched.h>
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#include "sched/sched.h"
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#ifdef CONFIG_SMP
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/****************************************************************************
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* Pre-processor Definitions
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****************************************************************************/
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#define IMPOSSIBLE_CPU 0xff
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/****************************************************************************
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* Public Functions
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****************************************************************************/
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/****************************************************************************
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* Name: sched_cpu_select
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*
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* Description:
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* Return the index to the CPU with the lowest priority running task,
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* possbily its IDLE task.
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*
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* Input Parameters:
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* affinity - The set of CPUs on which the thread is permitted to run.
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*
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* Returned Value:
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* Index of the CPU with the lowest priority running task
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*
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* Assumptions:
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* Called from within a critical section.
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*
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****************************************************************************/
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int sched_cpu_select(cpu_set_t affinity)
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{
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uint8_t minprio;
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int cpu;
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int i;
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/* Otherwise, find the CPU that is executing the lowest priority task
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* (possibly its IDLE task).
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*/
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minprio = SCHED_PRIORITY_MAX;
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cpu = IMPOSSIBLE_CPU;
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for (i = 0; i < CONFIG_SMP_NCPUS; i++)
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{
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/* If the thread permitted to run on this CPU? */
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if ((affinity & (1 << i)) != 0)
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{
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FAR struct tcb_s *rtcb = (FAR struct tcb_s *)g_assignedtasks[i].head;
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/* If this thread is executing its IDLE task, the use it. The
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* IDLE task is always the last task in the assigned task list.
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*/
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if (rtcb->flink == NULL)
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{
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/* The IDLE task should always be assigned to this CPU and have
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* a priority of zero.
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*/
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DEBUGASSERT(rtcb->sched_priority == 0);
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return i;
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}
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else if (rtcb->sched_priority < minprio)
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{
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DEBUGASSERT(rtcb->sched_priority > 0);
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minprio = rtcb->sched_priority;
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cpu = i;
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}
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}
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}
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DEBUGASSERT(cpu != IMPOSSIBLE_CPU);
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return cpu;
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}
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#endif /* CONFIG_SMP */
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