*
* \brief Simple cooperative multitasking scheduler.
*
- * \version $Id$
* \author Bernie Innocenti <bernie@codewiz.org>
* \author Stefano Fedrigo <aleph@develer.com>
*/
#define LOG_FORMAT KERN_LOG_FORMAT
#include <cfg/log.h>
-#include "cfg/cfg_arch.h" // ARCH_EMUL
#include "cfg/cfg_monitor.h"
#include <cfg/macros.h> // ROUND_UP2
#include <cfg/module.h>
#include <string.h> /* memset() */
+#define PROC_SIZE_WORDS (ROUND_UP2(sizeof(Process), sizeof(cpu_stack_t)) / sizeof(cpu_stack_t))
+
+/**
+ * CPU dependent context switching routines.
+ *
+ * Saving and restoring the context on the stack is done by a CPU-dependent
+ * support routine which usually needs to be written in assembly.
+ */
+EXTERN_C void asm_switch_context(cpu_stack_t **new_sp, cpu_stack_t **save_sp);
+
/*
* The scheduer tracks ready processes by enqueuing them in the
* ready list.
*
* \note Access to the list must occur while interrupts are disabled.
*/
-REGISTER List ProcReadyList;
+REGISTER List proc_ready_list;
/*
* Holds a pointer to the TCB of the currently running process.
*
* \note User applications should use proc_current() to retrieve this value.
*/
-REGISTER Process *CurrentProcess;
+REGISTER Process *current_process;
+
+/** The main process (the one that executes main()). */
+static struct Process main_process;
+
+#if CONFIG_KERN_HEAP
+
+/**
+ * Local heap dedicated to allocate the memory used by the processes.
+ */
+static HEAP_DEFINE_BUF(heap_buf, CONFIG_KERN_HEAP_SIZE);
+static Heap proc_heap;
-#if (ARCH & ARCH_EMUL)
/*
- * In some hosted environments, we must emulate the stack on the real
- * process stack to satisfy consistency checks in system libraries and
- * because some ABIs place trampolines on the stack.
+ * Keep track of zombie processes (processes that are exiting and need to
+ * release some resources).
*
- * Access to this list must be protected by PROC_ATOMIC().
+ * \note Access to the list must occur while kernel preemption is disabled.
*/
-List StackFreeList;
+static List zombie_list;
-#define NPROC 10
-cpu_stack_t proc_stacks[NPROC][(64 * 1024) / sizeof(cpu_stack_t)];
-#endif
-
-/** The main process (the one that executes main()). */
-struct Process MainProcess;
+#endif /* CONFIG_KERN_HEAP */
-
-static void proc_init_struct(Process *proc)
+static void proc_initStruct(Process *proc)
{
/* Avoid warning for unused argument. */
(void)proc;
#if CONFIG_KERN_PRI
proc->link.pri = 0;
#endif
-
}
MOD_DEFINE(proc);
void proc_init(void)
{
- LIST_INIT(&ProcReadyList);
+ LIST_INIT(&proc_ready_list);
-#if ARCH & ARCH_EMUL
- LIST_INIT(&StackFreeList);
- for (int i = 0; i < NPROC; i++)
- ADDTAIL(&StackFreeList, (Node *)proc_stacks[i]);
+#if CONFIG_KERN_HEAP
+ LIST_INIT(&zombie_list);
+ heap_init(&proc_heap, heap_buf, sizeof(heap_buf));
#endif
-
/*
* We "promote" the current context into a real process. The only thing we have
* to do is create a PCB and make it current. We don't need to setup the stack
* pointer because it will be written the first time we switch to another process.
*/
- proc_init_struct(&MainProcess);
- CurrentProcess = &MainProcess;
+ proc_initStruct(&main_process);
+ current_process = &main_process;
#if CONFIG_KERN_MONITOR
monitor_init();
- monitor_add(CurrentProcess, "main");
+ monitor_add(current_process, "main");
#endif
+ MOD_INIT(proc);
+}
+
+
+#if CONFIG_KERN_HEAP
+/**
+ * Free all the resources of all zombie processes previously added to the zombie
+ * list.
+ */
+static void proc_freeZombies(void)
+{
+ Process *proc;
+
+ while (1)
+ {
+ PROC_ATOMIC(proc = (Process *)list_remHead(&zombie_list));
+ if (proc == NULL)
+ return;
+
+ if (proc->flags & PF_FREESTACK)
+ {
+ PROC_ATOMIC(heap_freemem(&proc_heap, proc->stack_base,
+ proc->stack_size + PROC_SIZE_WORDS * sizeof(cpu_stack_t)));
+ }
+ }
+}
+
+/**
+ * Enqueue a process in the zombie list.
+ */
+static void proc_addZombie(Process *proc)
+{
+ Node *node;
#if CONFIG_KERN_PREEMPT
- preempt_init();
+ ASSERT(!proc_preemptAllowed());
#endif
- MOD_INIT(proc);
+#if CONFIG_KERN_PRI
+ node = &(proc)->link.link;
+#else
+ node = &(proc)->link;
+#endif
+ LIST_ASSERT_VALID(&zombie_list);
+ ADDTAIL(&zombie_list, node);
}
+#endif /* CONFIG_KERN_HEAP */
+
/**
* Create a new process, starting at the provided entry point.
*
+ *
+ * \note The function
+ * \code
+ * proc_new(entry, data, stacksize, stack)
+ * \endcode
+ * is a more convenient way to create a process, as you don't have to specify
+ * the name.
+ *
* \return Process structure of new created process
* if successful, NULL otherwise.
*/
struct Process *proc_new_with_name(UNUSED_ARG(const char *, name), void (*entry)(void), iptr_t data, size_t stack_size, cpu_stack_t *stack_base)
{
Process *proc;
- const size_t PROC_SIZE_WORDS = ROUND_UP2(sizeof(Process), sizeof(cpu_stack_t)) / sizeof(cpu_stack_t);
+ LOG_INFO("name=%s", name);
#if CONFIG_KERN_HEAP
bool free_stack = false;
-#endif
- LOG_INFO("name=%s", name);
-#if (ARCH & ARCH_EMUL)
- /* Ignore stack provided by caller and use the large enough default instead. */
- PROC_ATOMIC(stack_base = (cpu_stack_t *)list_remHead(&StackFreeList));
- ASSERT(stack_base);
+ /*
+ * Free up resources of a zombie process.
+ *
+ * We're implementing a kind of lazy garbage collector here for
+ * efficiency reasons: we can avoid to introduce overhead into another
+ * kernel task dedicated to free up resources (e.g., idle) and we're
+ * not introducing any overhead into the scheduler after a context
+ * switch (that would be *very* bad, because the scheduler runs with
+ * IRQ disabled).
+ *
+ * In this way we are able to release the memory of the zombie tasks
+ * without disabling IRQs and without introducing any significant
+ * overhead in any other kernel task.
+ */
+ proc_freeZombies();
- stack_size = CONFIG_KERN_MINSTACKSIZE;
-#elif CONFIG_KERN_HEAP
/* Did the caller provide a stack for us? */
if (!stack_base)
{
/* Did the caller specify the desired stack size? */
if (!stack_size)
- stack_size = CONFIG_KERN_MINSTACKSIZE;
+ stack_size = KERN_MINSTACKSIZE;
/* Allocate stack dinamically */
- if (!(stack_base = heap_alloc(stack_size)))
+ PROC_ATOMIC(stack_base =
+ (cpu_stack_t *)heap_allocmem(&proc_heap, stack_size));
+ if (stack_base == NULL)
return NULL;
free_stack = true;
}
-#else // !ARCH_EMUL && !CONFIG_KERN_HEAP
+#else // CONFIG_KERN_HEAP
/* Stack must have been provided by the user */
ASSERT_VALID_PTR(stack_base);
ASSERT(stack_size);
-#endif // !ARCH_EMUL && !CONFIG_KERN_HEAP
+#endif // CONFIG_KERN_HEAP
#if CONFIG_KERN_MONITOR
/*
ASSERT((uintptr_t)proc->stack % sizeof(cpu_aligned_stack_t) == 0);
stack_size -= PROC_SIZE_WORDS * sizeof(cpu_stack_t);
- proc_init_struct(proc);
+ proc_initStruct(proc);
proc->user_data = data;
-#if CONFIG_KERN_HEAP | CONFIG_KERN_MONITOR | (ARCH & ARCH_EMUL)
+#if CONFIG_KERN_HEAP | CONFIG_KERN_MONITOR
proc->stack_base = stack_base;
proc->stack_size = stack_size;
#if CONFIG_KERN_HEAP
proc->flags |= PF_FREESTACK;
#endif
#endif
+ proc->user_entry = entry;
+ CPU_CREATE_NEW_STACK(proc->stack);
- #if CONFIG_KERN_PREEMPT
-
- getcontext(&proc->context);
- proc->context.uc_stack.ss_sp = proc->stack;
- proc->context.uc_stack.ss_size = stack_size - 1;
- proc->context.uc_link = NULL;
- makecontext(&proc->context, (void (*)(void))proc_entry, 1, entry);
-
- #else // !CONFIG_KERN_PREEMPT
-
- CPU_CREATE_NEW_STACK(proc->stack, entry, proc_exit);
-
- #endif // CONFIG_KERN_PREEMPT
-
- #if CONFIG_KERN_MONITOR
- monitor_add(proc, name);
- #endif
+#if CONFIG_KERN_MONITOR
+ monitor_add(proc, name);
+#endif
/* Add to ready list */
ATOMIC(SCHED_ENQUEUE(proc));
*/
const char *proc_name(struct Process *proc)
{
- #if CONFIG_KERN_MONITOR
- return proc ? proc->monitor.name : "<NULL>";
- #else
- (void)proc;
- return "---";
- #endif
+#if CONFIG_KERN_MONITOR
+ return proc ? proc->monitor.name : "<NULL>";
+#else
+ (void)proc;
+ return "---";
+#endif
}
/// Return the name of the currently running process
*/
void proc_setPri(struct Process *proc, int pri)
{
- if (proc->link.pri == pri)
- return;
+ if (proc->link.pri == pri)
+ return;
- proc->link.pri = pri;
+ proc->link.pri = pri;
- if (proc != CurrentProcess)
- {
- proc_forbid();
- ATOMIC(sched_reenqueue(proc));
- proc_permit();
- }
+ if (proc != current_process)
+ ATOMIC(sched_reenqueue(proc));
}
#endif // CONFIG_KERN_PRI
+INLINE void proc_run(void)
+{
+ void (*entry)(void) = current_process->user_entry;
+
+ LOG_INFO("New process starting at %p", entry);
+ entry();
+}
+
+/**
+ * Entry point for all the processes.
+ */
+void proc_entry(void)
+{
+ /*
+ * Return from a context switch assumes interrupts are disabled, so
+ * we need to explicitly re-enable them as soon as possible.
+ */
+ IRQ_ENABLE;
+ /* Call the actual process's entry point */
+ proc_run();
+ proc_exit();
+}
+
/**
* Terminate the current process
*/
void proc_exit(void)
{
- LOG_INFO("%p:%s", CurrentProcess, proc_currentName());
+ LOG_INFO("%p:%s", current_process, proc_currentName());
#if CONFIG_KERN_MONITOR
- monitor_remove(CurrentProcess);
+ monitor_remove(current_process);
#endif
+ proc_forbid();
#if CONFIG_KERN_HEAP
/*
- * The following code is BROKEN.
- * We are freeing our own stack before entering proc_schedule()
- * BAJO: A correct fix would be to rearrange the scheduler with
- * an additional parameter which frees the old stack/process
- * after a context switch.
+ * Set the task as zombie, its resources will be freed in proc_new() in
+ * a lazy way, when another process will be created.
*/
- if (CurrentProcess->flags & PF_FREESTACK)
- heap_free(CurrentProcess->stack_base, CurrentProcess->stack_size);
- heap_free(CurrentProcess);
+ proc_addZombie(current_process);
#endif
+ current_process = NULL;
+ proc_permit();
-#if (ARCH & ARCH_EMUL)
- /* Reinsert process stack in free list */
- PROC_ATOMIC(ADDHEAD(&StackFreeList, (Node *)CurrentProcess->stack_base));
-
- /*
- * NOTE: At this point the first two words of what used
- * to be our stack contain a list node. From now on, we
- * rely on the compiler not reading/writing the stack.
- */
-#endif /* ARCH_EMUL */
-
- CurrentProcess = NULL;
proc_switch();
- /* not reached */
+
+ /* never reached */
+ ASSERT(0);
}
*/
iptr_t proc_currentUserData(void)
{
- return CurrentProcess->user_data;
+ return current_process->user_data;
+}
+
+/**
+ * Call the scheduler and eventually replace the current running process.
+ */
+void proc_schedule(void)
+{
+ Process *old_process = current_process;
+
+ IRQ_ASSERT_DISABLED();
+
+ /* Poll on the ready queue for the first ready process */
+ LIST_ASSERT_VALID(&proc_ready_list);
+ while (!(current_process = (struct Process *)list_remHead(&proc_ready_list)))
+ {
+ /*
+ * 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 proc_ready_list. 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.
+ * \todo If there was a way to write sig_wait() so that it does not
+ * disable interrupts while waiting, there would not be any
+ * reason to do this.
+ */
+ IRQ_ENABLE;
+ CPU_IDLE;
+ MEMORY_BARRIER;
+ IRQ_DISABLE;
+ }
+ /*
+ * Optimization: don't switch contexts when the active process has not
+ * changed.
+ */
+ if (LIKELY(current_process != old_process)) {
+ cpu_stack_t *dummy;
+
+ /*
+ * Save context of old process and switch to new process. If
+ * there is no old process, we save the old stack pointer into
+ * a dummy variable that we ignore. In fact, this happens only
+ * when the old process has just exited.
+ */
+ asm_switch_context(¤t_process->stack,
+ old_process ? &old_process->stack : &dummy);
+ }
+ /* This RET resumes the execution on the new process */
+ LOG_INFO("resuming %p:%s\n", current_process, proc_currentName());
}
projects / bertos.git / blobdiff