* Copyright 2008 Bernie Innocenti <bernie@codewiz.org>
* -->
*
- * \brief Simple realtime multitasking scheduler.
- * Context switching is only done cooperatively.
+ * \brief Simple preemptive multitasking scheduler.
*
- * \version $Id: proc.c 1616 2008-08-10 19:41:26Z bernie $
+ * All voluntary and preemptive context switching happens on exit from
+ * a common interrupt (signal) dispatcher. Preemption on quantum timeout
+ * is regulated by a soft-timer. Other kinds of preemption could happen
+ * if an interrupt sends a signal to a higher priority process (but this
+ * is still unimplemented).
+ *
+ * In the POSIX implementaiton, context switching is done by the portable
+ * SVR4 swapcontext() facility.
+ *
+ * \version $Id$
* \author Bernie Innocenti <bernie@codewiz.org>
*/
+#include "cfg/cfg_proc.h"
+
+#if CONFIG_KERN_PREEMPT
+
#include "proc_p.h"
#include "proc.h"
+#include "idle.h"
#include <kern/irq.h>
+#include <kern/monitor.h>
#include <cpu/frame.h> // CPU_IDLE
+#include <cpu/irq.h> // IRQ_DISABLE()...
#include <drv/timer.h>
#include <cfg/module.h>
+#include <cfg/depend.h> // CONFIG_DEPEND()
+// Check config dependencies
+CONFIG_DEPEND(CONFIG_KERN_PREEMPT, CONFIG_KERN && CONFIG_TIMER_EVENTS && CONFIG_KERN_IRQ);
-/*
- * The time sharing scheduler forces a task switch when the current
- * process has exhausted its quantum.
- */
-uint16_t Quantum;
-
-Timer preempt_timer;
+MOD_DEFINE(preempt)
-/**
- * Disable preemptive task switching.
- *
- * The scheduler maintains a per-process nesting counter. Task switching is
- * effectively re-enabled only when the number of calls to proc_permit()
- * matches the number of calls to proc_forbid().
- *
- * Calling functions that could sleep while task switching is disabled
- * is dangerous, although supported. Preemptive task switching is
- * resumed while the process is sleeping and disabled again as soon as
- * it wakes up again.
- *
- * \sa proc_permit()
- */
-void proc_forbid(void)
-{
- /* No need to protect against interrupts here. */
- ++CurrentProcess->forbid_cnt;
-}
+/// Global preemption disabling nesting counter
+cpu_atomic_t _preempt_forbid_cnt;
-/**
- * Re-enable preemptive task switching.
- *
- * \sa proc_forbid()
- */
-void proc_permit(void)
-{
- /* No need to protect against interrupts here. */
- --CurrentProcess->forbid_cnt;
-}
+static Timer preempt_timer;
-void proc_preempt(void)
+void proc_schedule(void)
{
- TRACE;
+ IRQ_DISABLE;
- ATOMIC(LIST_ASSERT_VALID(&ProcReadyList));
+ ASSERT(proc_preemptAllowed());
+ LIST_ASSERT_VALID(&ProcReadyList);
+ CurrentProcess = (struct Process *)list_remHead(&ProcReadyList);
+ ASSERT2(CurrentProcess, "no idle proc?");
- TRACEMSG("hello1");
- IRQ_DISABLE;
- /* Poll on the ready queue for the first ready process */
- while (!(CurrentProcess = (struct Process *)list_remHead(&ProcReadyList)))
- {
- //TRACEMSG("hello2");
- /*
- * Make sure we physically reenable interrupts here, no matter what
- * the current task status is. This is important because if we
- * are idle-spinning, we must allow interrupts, otherwise no
- * process will ever wake up.
- *
- * During idle-spinning, an interrupt can occur and it may
- * modify \p ProcReadyList. To ensure that compiler reload this
- * variable every while cycle we call CPU_MEMORY_BARRIER.
- * The memory barrier ensure that all variables used in this context
- * are reloaded.
- */
- IRQ_ENABLE;
- //FIXME: calls Qt stuff from sighandler! CPU_IDLE;
- MEMORY_BARRIER;
- IRQ_DISABLE;
- //TRACEMSG("hello3");
- }
IRQ_ENABLE;
- TRACEMSG("hello4");
+
+ TRACEMSG("launching %p:%s", CurrentProcess, proc_currentName());
}
-void proc_preempt_timer(UNUSED_ARG(void *, param))
+void proc_preempt(UNUSED_ARG(void *, param))
{
- IRQ_DISABLE;
- if (CurrentProcess)
+ if (proc_preemptAllowed())
{
- TRACEMSG("preempting %p:%s", CurrentProcess, CurrentProcess->monitor.name);
+ IRQ_DISABLE;
+
+ #if CONFIG_KERN_PRI
+ Process *rival = (Process *)LIST_HEAD(&ProcReadyList);
+ if (rival && rival->link.pri >= CurrentProcess->link.pri)
+ {
+ #endif
+
+ TRACEMSG("preempting %p:%s", CurrentProcess, proc_currentName());
+
+// FIXME: this still breaks havoc, probably because of some reentrancy issue
+#if 0
SCHED_ENQUEUE(CurrentProcess);
+ proc_schedule();
+#endif
+ #if CONFIG_KERN_PRI
+ }
+ #endif
+
IRQ_ENABLE;
- proc_preempt();
}
- IRQ_ENABLE;
timer_setDelay(&preempt_timer, CONFIG_KERN_QUANTUM);
timer_add(&preempt_timer);
}
-void proc_schedule(void)
+void proc_switch(void)
{
- TRACE;
+ ATOMIC(LIST_ASSERT_VALID(&ProcReadyList));
+ TRACEMSG("%p:%s", CurrentProcess, proc_currentName());
+ ATOMIC(LIST_ASSERT_VALID(&ProcReadyList));
+
+ /* Sleeping with IRQs disabled or preemption forbidden is illegal */
+ IRQ_ASSERT_ENABLED();
+ ASSERT(proc_preemptAllowed());
- // Will invoke proc_preempt() in interrupt context
+ // Will invoke proc_switch() in interrupt context
kill(0, SIGUSR1);
}
void proc_yield(void)
{
- ATOMIC(SCHED_ENQUEUE(CurrentProcess));
+ TRACEMSG("%p:%s", CurrentProcess, proc_currentName());
- proc_schedule();
+ IRQ_DISABLE;
+ SCHED_ENQUEUE(CurrentProcess);
+ IRQ_ENABLE;
+
+ proc_switch();
}
void proc_entry(void (*user_entry)(void))
MOD_CHECK(irq);
MOD_CHECK(timer);
- irq_register(SIGUSR1, proc_preempt);
+ irq_register(SIGUSR1, proc_schedule);
- timer_setSoftint(&preempt_timer, proc_preempt_timer, NULL);
+ timer_setSoftint(&preempt_timer, proc_preempt, NULL);
timer_setDelay(&preempt_timer, CONFIG_KERN_QUANTUM);
timer_add(&preempt_timer);
+
+ idle_init();
+
+ MOD_INIT(preempt);
}
+
+#endif // CONFIG_KERN_PREEMPT
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