proc: Use a global forbid count;

[bertos.git] / bertos / kern / preempt.c

diff --git a/bertos/kern/preempt.c b/bertos/kern/preempt.c
index 9af6c0d1b402a973cc144532c15c2f1ae5d15d2f..756a38fe0b89d1073b0c4585f8b702050877901a 100644 (file)
--- a/bertos/kern/preempt.c
+++ b/bertos/kern/preempt.c
@@ -29,8 +29,7 @@
  * 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 $
  * \author Bernie Innocenti <bernie@codewiz.org>
@@ -40,95 +39,48 @@
 #include "proc.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>
 
 
-/*
- * The time sharing scheduler forces a task switch when the current
- * process has exhausted its quantum.
- */
-uint16_t Quantum;
+int preempt_forbid_cnt;
 
 Timer preempt_timer;
 
-/**
- * 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;
-}
-
-/**
- * Re-enable preemptive task switching.
- *
- * \sa proc_forbid()
- */
-void proc_permit(void)
-{
-       /* No need to protect against interrupts here. */
-       --CurrentProcess->forbid_cnt;
-}
-
 
 void proc_preempt(void)
 {
-       TRACE;
+       IRQ_DISABLE;
 
-       ATOMIC(LIST_ASSERT_VALID(&ProcReadyList));
+       LIST_ASSERT_VALID(&ProcReadyList);
+       CurrentProcess = (struct Process *)list_remHead(&ProcReadyList);
+       LIST_ASSERT_VALID(&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("new proc: %p:%s", CurrentProcess, CurrentProcess ? CurrentProcess->monitor.name : "---");
+       monitor_report();
 }
 
 void proc_preempt_timer(UNUSED_ARG(void *, param))
 {
+       /* Abort if task preemption is disabled */
+       if (preempt_forbid_cnt)
+               return;
+
        IRQ_DISABLE;
-       if (CurrentProcess)
+/*
+       if (!CurrentProcess->forbid_cnt)
        {
                TRACEMSG("preempting %p:%s", CurrentProcess, CurrentProcess->monitor.name);
                SCHED_ENQUEUE(CurrentProcess);
-               IRQ_ENABLE;
                proc_preempt();
        }
+*/
        IRQ_ENABLE;
 
        timer_setDelay(&preempt_timer, CONFIG_KERN_QUANTUM);
@@ -137,7 +89,13 @@ void proc_preempt_timer(UNUSED_ARG(void *, param))
 
 void proc_schedule(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 */
+       ASSERT_IRQ_ENABLED();
+       ASSERT(preempt_forbid_cnt == 0);
 
        // Will invoke proc_preempt() in interrupt context
        kill(0, SIGUSR1);
@@ -145,7 +103,11 @@ void proc_schedule(void)
 
 void proc_yield(void)
 {
-       ATOMIC(SCHED_ENQUEUE(CurrentProcess));
+       TRACEMSG("%p:%s", CurrentProcess, proc_currentName());
+
+       IRQ_DISABLE;
+       SCHED_ENQUEUE(CurrentProcess);
+       IRQ_ENABLE;
 
        proc_schedule();
 }
@@ -156,6 +118,30 @@ void proc_entry(void (*user_entry)(void))
        proc_exit();
 }
 
+
+static cpustack_t idle_stack[CONFIG_PROC_DEFSTACKSIZE / sizeof(cpustack_t)];
+
+// FIXME: move this to kern/idle.c
+/**
+ * The idle process
+ *
+ * This process never dies and never sleeps.  It's also quite lazy, apathic
+ * and a bit antisocial.
+ *
+ * Having an idle process costs some stack space, but simplifies the
+ * interrupt-driven preemption logic because there is always a user
+ * context to which we can return.
+ */
+static NORETURN void idle(void)
+{
+       for (;;)
+       {
+               TRACE;
+               //monitor_report();
+               proc_yield(); // FIXME: CPU_IDLE
+       }
+}
+
 void preempt_init(void)
 {
        MOD_CHECK(irq);
@@ -166,4 +152,6 @@ void preempt_init(void)
        timer_setSoftint(&preempt_timer, proc_preempt_timer, NULL);
        timer_setDelay(&preempt_timer, CONFIG_KERN_QUANTUM);
        timer_add(&preempt_timer);
+
+       proc_new(idle, NULL, sizeof(idle_stack), idle_stack);
 }