* invalidate any other reasons why the executable file might be covered by
* the GNU General Public License.
*
- * Copyright 2001, 2004 Develer S.r.l. (http://www.develer.com/)
- * Copyright 1999, 2000, 2001, 2008 Bernie Innocenti <bernie@codewiz.org>
+ * \brief Simple preemptive multitasking scheduler.
+ *
+ * Preemption is explicitly regulated at the exit of each interrupt service
+ * routine (ISR). Each task obtains a time quantum as soon as it is scheduled
+ * on the CPU and its quantum is decremented at each clock tick. The frequency
+ * of the timer determines the system tick granularity and CONFIG_KERN_QUANTUM
+ * the time sharing interval.
+ *
+ * When the quantum expires the handler proc_needPreempt() checks if the
+ * preemption is enabled and in this case proc_schedule() is called, that
+ * possibly replaces the current running thread with a different one.
+ *
+ * The preemption can be disabled or enabled via proc_forbid() and
+ * proc_permit() primitives. This is implemented using a global atomic counter.
+ * When the counter is greater than 0 the task cannot be preempted; only when
+ * the counter reaches 0 the task can be preempted again.
+ *
+ * Preemption-disabled sections may be nested. The preemption will be
+ * re-enabled when the outermost preemption-disabled section completes.
+ *
+ * The voluntary preemption still happens via proc_switch() or proc_yield().
+ * The first one assumes the current process has been already added to a
+ * private wait queue (e.g., on a semaphore or a signal), while the second one
+ * takes care of adding the process into the ready queue.
+ *
+ * Context switch is done by CPU-dependent support routines. In case of a
+ * voluntary preemption the context switch routine must take care of
+ * saving/restoring only the callee-save registers (the voluntary-preemption is
+ * actually a function call). The kernel-preemption always happens inside a
+ * signal/interrupt context and it must take care of saving all registers. For
+ * this, in the entry point of each ISR the caller-save registers must be
+ * saved. In the ISR exit point, if the context switch must happen, we switch
+ * to user-context and call the same voluntary context switch routine that take
+ * care of saving/restoring also the callee-save registers. On resume from the
+ * switch, the interrupt exit point moves back to interrupt-context, resumes
+ * the caller-save registers (saved in the ISR entry point) and return from the
+ * interrupt-context.
+ *
+ * \note Thread priority (if enabled by CONFIG_KERN_PRI) defines the order in
+ * the \p proc_ready_list and the capability to deschedule a running process. A
+ * low-priority thread can't preempt a high-priority thread.
+ *
+ * A high-priority process can preempt a low-priority process immediately (it
+ * will be descheduled and replaced in the interrupt exit point). Processes
+ * running at the same priority can be descheduled when they expire the time
+ * quantum.
+ *
+ * \note Sleeping while preemption is disabled fallbacks to a busy-wait sleep.
+ * Voluntary preemption when preemption is disabled raises a kernel bug.
+ *
* -->
*
- * \brief Simple cooperative multitasking scheduler.
+ * \brief Simple cooperative and preemptive multitasking scheduler.
*
- * \version $Id$
* \author Bernie Innocenti <bernie@codewiz.org>
* \author Stefano Fedrigo <aleph@develer.com>
+ * \author Andrea Righi <arighi@develer.com>
*/
#include "proc_p.h"
#include "proc.h"
-#include "cfg/cfg_arch.h" // ARCH_EMUL
#include "cfg/cfg_proc.h"
+#define LOG_LEVEL KERN_LOG_LEVEL
+#define LOG_FORMAT KERN_LOG_FORMAT
+#include <cfg/log.h>
+
#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))
+
/*
* 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
+#endif /* CONFIG_KERN_HEAP */
-/** The main process (the one that executes main()). */
-struct Process MainProcess;
+/*
+ * Check if the process context switch can be performed directly by the
+ * architecture-dependent asm_switch_context() or if it must be delayed
+ * because we're in the middle of an ISR.
+ *
+ * Return true if asm_switch_context() can be executed, false
+ * otherwise.
+ *
+ * NOTE: if an architecture does not implement IRQ_RUNNING() this function
+ * always returns true.
+ */
+#define CONTEXT_SWITCH_FROM_ISR() (!IRQ_RUNNING())
+
+/*
+ * Save context of old process and switch to new process.
+ */
+static void proc_context_switch(Process *next, Process *prev)
+{
+ cpu_stack_t *dummy;
+ if (UNLIKELY(next == prev))
+ return;
+ /*
+ * 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(&next->stack, prev ? &prev->stack : &dummy);
+}
-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
- TRACEMSG("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
/*
proc = (Process *)stack_base;
proc->stack = stack_base + PROC_SIZE_WORDS;
// On some architecture stack should be aligned, so we do it.
- proc->stack = (void *)proc->stack + (sizeof(cpu_aligned_stack_t) - ((long)proc->stack % sizeof(cpu_stack_aligned_t)));
+ proc->stack = (cpu_stack_t *)((uintptr_t)proc->stack + (sizeof(cpu_aligned_stack_t) - ((uintptr_t)proc->stack % sizeof(cpu_aligned_stack_t))));
if (CPU_SP_ON_EMPTY_SLOT)
proc->stack++;
}
{
proc = (Process *)(stack_base + stack_size / sizeof(cpu_stack_t) - PROC_SIZE_WORDS);
// On some architecture stack should be aligned, so we do it.
- proc->stack = (void *)proc - ((long)proc % sizeof(cpu_aligned_stack_t));
+ proc->stack = (cpu_stack_t *)((uintptr_t)proc - ((uintptr_t)proc % sizeof(cpu_aligned_stack_t)));
if (CPU_SP_ON_EMPTY_SLOT)
proc->stack--;
}
+ /* Ensure stack is aligned */
+ ASSERT((uintptr_t)proc->stack % sizeof(cpu_aligned_stack_t) == 0);
- stack_size = stack_size - PROC_SIZE_WORDS;
- proc_init_struct(proc);
+ stack_size -= PROC_SIZE_WORDS * sizeof(cpu_stack_t);
+ 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
- {
- size_t i;
-
- /* Initialize process stack frame */
- CPU_PUSH_CALL_FRAME(proc->stack, proc_exit);
- CPU_PUSH_CALL_FRAME(proc->stack, entry);
-
- /* Push a clean set of CPU registers for asm_switch_context() */
- for (i = 0; i < CPU_SAVED_REGS_CNT; i++)
- CPU_PUSH_WORD(proc->stack, CPU_REG_INIT_VALUE(i));
- }
- #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)
{
- TRACEMSG("%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));
+ proc_switch();
- /*
- * 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 */
+ /* never reached */
+ ASSERT(0);
+}
- CurrentProcess = NULL;
- proc_switch();
- /* not reached */
+/**
+ * Call the scheduler and eventually replace the current running process.
+ */
+static 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;
+ }
+ if (CONTEXT_SWITCH_FROM_ISR())
+ proc_context_switch(current_process, old_process);
+ /* This RET resumes the execution on the new process */
+ LOG_INFO("resuming %p:%s\n", current_process, proc_currentName());
}
+#if CONFIG_KERN_PREEMPT
+/* Global preemption nesting counter */
+cpu_atomic_t preempt_count;
+
+/*
+ * The time sharing interval: when a process is scheduled on a CPU it gets an
+ * amount of CONFIG_KERN_QUANTUM clock ticks. When these ticks expires and
+ * preemption is enabled a new process is selected to run.
+ */
+int _proc_quantum;
/**
- * Get the pointer to the user data of the current process
+ * Check if we need to schedule another task
*/
-iptr_t proc_currentUserData(void)
+bool proc_needPreempt(void)
+{
+ if (UNLIKELY(current_process == NULL))
+ return false;
+ if (!proc_preemptAllowed())
+ return false;
+ if (LIST_EMPTY(&proc_ready_list))
+ return false;
+ return preempt_quantum() ? prio_next() > prio_curr() :
+ prio_next() >= prio_curr();
+}
+
+/**
+ * Preempt the current task.
+ */
+void proc_preempt(void)
+{
+ IRQ_ASSERT_DISABLED();
+ ASSERT(current_process);
+
+ /* Perform the kernel preemption */
+ LOG_INFO("preempting %p:%s\n", current_process, proc_currentName());
+ /* We are inside a IRQ context, so ATOMIC is not needed here */
+ SCHED_ENQUEUE(current_process);
+ preempt_reset_quantum();
+ proc_schedule();
+}
+#endif /* CONFIG_KERN_PREEMPT */
+
+/* Immediately switch to a particular process */
+static void proc_switchTo(Process *proc)
{
- return CurrentProcess->user_data;
+ Process *old_process = current_process;
+
+ SCHED_ENQUEUE(current_process);
+ preempt_reset_quantum();
+ current_process = proc;
+ proc_context_switch(current_process, old_process);
+}
+
+/**
+ * Give the control of the CPU to another process.
+ *
+ * \note Assume the current process has been already added to a wait queue.
+ *
+ * \warning This should be considered an internal kernel function, even if it
+ * is allowed, usage from application code is strongly discouraged.
+ */
+void proc_switch(void)
+{
+ ASSERT(proc_preemptAllowed());
+ ATOMIC(
+ preempt_reset_quantum();
+ proc_schedule();
+ );
+}
+
+/**
+ * Immediately wakeup a process, dispatching it to the CPU.
+ */
+void proc_wakeup(Process *proc)
+{
+ ASSERT(proc_preemptAllowed());
+ ASSERT(current_process);
+ IRQ_ASSERT_DISABLED();
+
+ if (prio_proc(proc) >= prio_curr())
+ proc_switchTo(proc);
+ else
+ SCHED_ENQUEUE_HEAD(proc);
+}
+
+/**
+ * Voluntarily release the CPU.
+ */
+void proc_yield(void)
+{
+ Process *proc;
+
+ /*
+ * Voluntary preemption while preemption is disabled is considered
+ * illegal, as not very useful in practice.
+ *
+ * ASSERT if it happens.
+ */
+ ASSERT(proc_preemptAllowed());
+ IRQ_ASSERT_ENABLED();
+
+ IRQ_DISABLE;
+ proc = (struct Process *)list_remHead(&proc_ready_list);
+ if (proc)
+ proc_switchTo(proc);
+ IRQ_ENABLE;
}
projects / bertos.git / blobdiff