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/*
ChibiOS - Copyright (C) 2006..2016 Giovanni Di Sirio.
This file is part of ChibiOS.
ChibiOS is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3 of the License, or
(at your option) any later version.
ChibiOS is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
/**
* @file chpreempt.c
* @brief Preemption enforcement code.
*
* @addtogroup preemption_enforcement
* @details This modules export hook macros required for implementing
* a preemptive round robin mode for threads at the same priority
* level.<br>
* This method is alternative to the ChibiOS/RT native implementation
* which is not compatible with the tick-less mode, however, this
* timers-based solution can decrease threads context-switch
* performance because the added overhead.
* @note This file is not included automatically by @p ch.h, you need
* to:
* - Define @p CH_CFG_ROUND_ROBIN_QUANTUM in chconf.h. It is the
* time quantum in ticks.
* - Include @p chpreempt.h from @p chconf.h.
* - Add all the macros and functions to the appropriate hooks in
* chconf.h.
* - Explicitely add @p chpreempt.c to your makefile.
* .
*/
#include "ch.h"
/*===========================================================================*/
/* Module exported variables. */
/*===========================================================================*/
/*===========================================================================*/
/* Module local types. */
/*===========================================================================*/
/*===========================================================================*/
/* Module local variables. */
/*===========================================================================*/
/*===========================================================================*/
/* Module local functions. */
/*===========================================================================*/
static void preempt_cb(void *p) {
(void)p;
}
/*===========================================================================*/
/* Module exported functions. */
/*===========================================================================*/
/**
* @brief Hook code for system initialization.
*
* @notapi
*/
void ch_preempt_system_init(void) {
chVTObjectInit(&ch.preempt_vt);
}
/**
* @brief Hook code for context switch.
*
* @notapi
*/
void ch_preempt_thread_switch(void) {
chVTSetI(&ch.preempt_vt, CH_CFG_ROUND_ROBIN_QUANTUM, preempt_cb, NULL);
}
/**
* @brief Evaluates if preemption is required.
* @details The decision is taken by comparing the relative priorities and
* depending on the state of the round robin timeout counter.
* @note Not a user function, it is meant to be invoked by the scheduler
* itself or from within the port layer.
*
* @retval true if there is a thread that must go in running state
* immediately.
* @retval false if preemption is not required.
*
* @special
*/
bool chSchIsPreemptionRequired(void) {
tprio_t p1 = firstprio(&ch.rlist.queue);
tprio_t p2 = currp->prio;
/* If the running thread has not reached its time quantum, reschedule only
if the first thread on the ready queue has a higher priority.
Otherwise, if the running thread has used up its time quantum, reschedule
if the first thread on the ready queue has equal or higher priority.*/
return chVTIsArmed(&ch.preempt_vt) ? (p1 > p2) : (p1 >= p2);
}
/**
* @brief Switches to the first thread on the runnable queue.
* @details The current thread is positioned in the ready list behind or
* ahead of all threads having the same priority depending on
* if it used its whole time slice.
* @note Not a user function, it is meant to be invoked by the scheduler
* itself or from within the port layer.
*
* @special
*/
void chSchDoReschedule(void) {
thread_t *otp = currp;
/* Picks the first thread from the ready queue and makes it current.*/
currp = queue_fifo_remove(&ch.rlist.queue);
currp->state = CH_STATE_CURRENT;
/* Handling idle-leave hook.*/
if (otp->prio == IDLEPRIO) {
CH_CFG_IDLE_LEAVE_HOOK();
}
/* There are two different scenarios to handle on preemption: time quantum
elapsed or not.*/
if (!chVTIsArmed(&ch.preempt_vt)) {
/* The thread consumed its time quantum so it is enqueued behind threads
with same priority level, however, it acquires a new time quantum.*/
otp = chSchReadyI(otp);
}
else {
/* The thread didn't consume all its time quantum so it is put ahead of
threads with equal priority and does not acquire a new time quantum.*/
otp = chSchReadyAheadI(otp);
}
/* Swap operation as tail call.*/
chSysSwitch(currp, otp);
}
/** @} */
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