cleanups, speedups and fixes. Added support for non-current set_cpus_allowed().

arch/i386/kernel/i8259.c

@@ -79,7 +79,6 @@ BUILD_16_IRQS(0xc) BUILD_16_IRQS(0xd)
  * through the ICC by us (IPIs)
  */
 #ifdef CONFIG_SMP
-BUILD_SMP_INTERRUPT(task_migration_interrupt,TASK_MIGRATION_VECTOR)
 BUILD_SMP_INTERRUPT(reschedule_interrupt,RESCHEDULE_VECTOR)
 BUILD_SMP_INTERRUPT(invalidate_interrupt,INVALIDATE_TLB_VECTOR)
 BUILD_SMP_INTERRUPT(call_function_interrupt,CALL_FUNCTION_VECTOR)
@@ -474,9 +473,6 @@ void __init init_IRQ(void)
 	 */
 	set_intr_gate(RESCHEDULE_VECTOR, reschedule_interrupt);
 
-	/* IPI for task migration */
-	set_intr_gate(TASK_MIGRATION_VECTOR, task_migration_interrupt);
-
 	/* IPI for invalidation */
 	set_intr_gate(INVALIDATE_TLB_VECTOR, invalidate_interrupt);
 

arch/i386/kernel/smp.c

@@ -485,35 +485,6 @@ void flush_tlb_all(void)
 	do_flush_tlb_all_local();
 }
 
-static spinlock_t migration_lock = SPIN_LOCK_UNLOCKED;
-static task_t *new_task;
-
-/*
- * This function sends a 'task migration' IPI to another CPU.
- * Must be called from syscall contexts, with interrupts *enabled*.
- */
-void smp_migrate_task(int cpu, task_t *p)
-{
-	/*
-	 * The target CPU will unlock the migration spinlock:
-	 */
-	_raw_spin_lock(&migration_lock);
-	new_task = p;
-	send_IPI_mask(1 << cpu, TASK_MIGRATION_VECTOR);
-}
-
-/*
- * Task migration callback.
- */
-asmlinkage void smp_task_migration_interrupt(void)
-{
-	task_t *p;
-
-	ack_APIC_irq();
-	p = new_task;
-	_raw_spin_unlock(&migration_lock);
-	sched_task_migrated(p);
-}
 /*
  * this function sends a 'reschedule' IPI to another CPU.
  * it goes straight through and wastes no time serializing

fs/pipe.c

@@ -116,7 +116,7 @@ pipe_read(struct file *filp, char *buf, size_t count, loff_t *ppos)
 		 * writers synchronously that there is more
 		 * room.
 		 */
-		wake_up_interruptible_sync(PIPE_WAIT(*inode));
+		wake_up_interruptible(PIPE_WAIT(*inode));
 		if (!PIPE_EMPTY(*inode))
 			BUG();
 		goto do_more_read;
@@ -214,7 +214,7 @@ pipe_write(struct file *filp, const char *buf, size_t count, loff_t *ppos)
 			 * is going to give up this CPU, so it doesnt have
 			 * to do idle reschedules.
 			 */
-			wake_up_interruptible_sync(PIPE_WAIT(*inode));
+			wake_up_interruptible(PIPE_WAIT(*inode));
 			PIPE_WAITING_WRITERS(*inode)++;
 			pipe_wait(inode);
 			PIPE_WAITING_WRITERS(*inode)--;

include/asm-i386/hw_irq.h

@@ -35,14 +35,13 @@
  *  into a single vector (CALL_FUNCTION_VECTOR) to save vector space.
  *  TLB, reschedule and local APIC vectors are performance-critical.
  *
- *  Vectors 0xf0-0xf9 are free (reserved for future Linux use).
+ *  Vectors 0xf0-0xfa are free (reserved for future Linux use).
  */
 #define SPURIOUS_APIC_VECTOR	0xff
 #define ERROR_APIC_VECTOR	0xfe
 #define INVALIDATE_TLB_VECTOR	0xfd
 #define RESCHEDULE_VECTOR	0xfc
-#define TASK_MIGRATION_VECTOR	0xfb
-#define CALL_FUNCTION_VECTOR	0xfa
+#define CALL_FUNCTION_VECTOR	0xfb
 
 /*
  * Local APIC timer IRQ vector is on a different priority level,

include/linux/init_task.h

@@ -52,6 +52,8 @@
     mm:			NULL,						\
     active_mm:		&init_mm,					\
     run_list:		LIST_HEAD_INIT(tsk.run_list),			\
+    migration_list:	LIST_HEAD_INIT(tsk.migration_list),		\
+    migration_sem:	__MUTEX_INITIALIZER(tsk.migration_sem),		\
     time_slice:		HZ,						\
     next_task:		&tsk,						\
     prev_task:		&tsk,						\

include/linux/sched.h

@@ -150,8 +150,7 @@ extern void update_process_times(int user);
 extern void update_one_process(struct task_struct *p, unsigned long user,
 			       unsigned long system, int cpu);
 extern void scheduler_tick(int user_tick, int system);
-extern void sched_task_migrated(struct task_struct *p);
-extern void smp_migrate_task(int cpu, task_t *task);
+extern void migration_init(void);
 extern unsigned long cache_decay_ticks;
 
 
@@ -286,6 +285,10 @@ struct task_struct {
 
 	wait_queue_head_t wait_chldexit;	/* for wait4() */
 	struct completion *vfork_done;		/* for vfork() */
+
+	list_t migration_list;
+	struct semaphore migration_sem;
+
 	unsigned long rt_priority;
 	unsigned long it_real_value, it_prof_value, it_virt_value;
 	unsigned long it_real_incr, it_prof_incr, it_virt_incr;
@@ -382,7 +385,12 @@ do { if (atomic_dec_and_test(&(tsk)->usage)) __put_task_struct(tsk); } while(0)
  */
 #define _STK_LIM	(8*1024*1024)
 
+#if CONFIG_SMP
 extern void set_cpus_allowed(task_t *p, unsigned long new_mask);
+#else
+# define set_cpus_allowed(p, new_mask) do { } while (0)
+#endif
+
 extern void set_user_nice(task_t *p, long nice);
 extern int task_prio(task_t *p);
 extern int task_nice(task_t *p);
@@ -460,7 +468,6 @@ extern unsigned long prof_len;
 extern unsigned long prof_shift;
 
 extern void FASTCALL(__wake_up(wait_queue_head_t *q, unsigned int mode, int nr));
-extern void FASTCALL(__wake_up_sync(wait_queue_head_t *q, unsigned int mode, int nr));
 extern void FASTCALL(sleep_on(wait_queue_head_t *q));
 extern long FASTCALL(sleep_on_timeout(wait_queue_head_t *q,
 				      signed long timeout));
@@ -474,13 +481,9 @@ extern void FASTCALL(sched_exit(task_t * p));
 #define wake_up(x)			__wake_up((x),TASK_UNINTERRUPTIBLE | TASK_INTERRUPTIBLE, 1)
 #define wake_up_nr(x, nr)		__wake_up((x),TASK_UNINTERRUPTIBLE | TASK_INTERRUPTIBLE, nr)
 #define wake_up_all(x)			__wake_up((x),TASK_UNINTERRUPTIBLE | TASK_INTERRUPTIBLE, 0)
-#define wake_up_sync(x)			__wake_up_sync((x),TASK_UNINTERRUPTIBLE | TASK_INTERRUPTIBLE, 1)
-#define wake_up_sync_nr(x, nr)		__wake_up_sync((x),TASK_UNINTERRUPTIBLE | TASK_INTERRUPTIBLE, nr)
 #define wake_up_interruptible(x)	__wake_up((x),TASK_INTERRUPTIBLE, 1)
 #define wake_up_interruptible_nr(x, nr)	__wake_up((x),TASK_INTERRUPTIBLE, nr)
 #define wake_up_interruptible_all(x)	__wake_up((x),TASK_INTERRUPTIBLE, 0)
-#define wake_up_interruptible_sync(x)	__wake_up_sync((x),TASK_INTERRUPTIBLE, 1)
-#define wake_up_interruptible_sync_nr(x) __wake_up_sync((x),TASK_INTERRUPTIBLE,  nr)
 asmlinkage long sys_wait4(pid_t pid,unsigned int * stat_addr, int options, struct rusage * ru);
 
 extern int in_group_p(gid_t);

init/main.c

@@ -413,7 +413,12 @@ static void __init do_initcalls(void)
  */
 static void __init do_basic_setup(void)
 {
-
+	/*
+	 * Let the per-CPU migration threads start up:
+	 */
+#if CONFIG_SMP
+	migration_init();
+#endif
 	/*
 	 * Tell the world that we're going to be the grim
 	 * reaper of innocent orphaned children.

kernel/ksyms.c

@@ -443,7 +443,6 @@ EXPORT_SYMBOL(iomem_resource);
 /* process management */
 EXPORT_SYMBOL(complete_and_exit);
 EXPORT_SYMBOL(__wake_up);
-EXPORT_SYMBOL(__wake_up_sync);
 EXPORT_SYMBOL(wake_up_process);
 EXPORT_SYMBOL(sleep_on);
 EXPORT_SYMBOL(sleep_on_timeout);
@@ -458,6 +457,9 @@ EXPORT_SYMBOL(sys_sched_yield);
 EXPORT_SYMBOL(set_user_nice);
 EXPORT_SYMBOL(task_nice);
 EXPORT_SYMBOL_GPL(idle_cpu);
+#if CONFIG_SMP
+EXPORT_SYMBOL_GPL(set_cpus_allowed);
+#endif
 EXPORT_SYMBOL(jiffies);
 EXPORT_SYMBOL(xtime);
 EXPORT_SYMBOL(do_gettimeofday);

kernel/sched.c

@@ -16,12 +16,12 @@
 #include <linux/nmi.h>
 #include <linux/init.h>
 #include <asm/uaccess.h>
+#include <linux/highmem.h>
 #include <linux/smp_lock.h>
+#include <asm/mmu_context.h>
 #include <linux/interrupt.h>
 #include <linux/completion.h>
-#include <asm/mmu_context.h>
 #include <linux/kernel_stat.h>
-#include <linux/highmem.h>
 
 /*
  * Priority of a process goes from 0 to 139. The 0-99
@@ -127,8 +127,6 @@ typedef struct runqueue runqueue_t;
 
 struct prio_array {
 	int nr_active;
-	spinlock_t *lock;
-	runqueue_t *rq;
 	unsigned long bitmap[BITMAP_SIZE];
 	list_t queue[MAX_PRIO];
 };
@@ -146,6 +144,8 @@ struct runqueue {
 	task_t *curr, *idle;
 	prio_array_t *active, *expired, arrays[2];
 	int prev_nr_running[NR_CPUS];
+	task_t *migration_thread;
+	list_t migration_queue;
 } ____cacheline_aligned;
 
 static struct runqueue runqueues[NR_CPUS] __cacheline_aligned;
@@ -156,23 +156,23 @@ static struct runqueue runqueues[NR_CPUS] __cacheline_aligned;
 #define cpu_curr(cpu)		(cpu_rq(cpu)->curr)
 #define rt_task(p)		((p)->prio < MAX_RT_PRIO)
 
-static inline runqueue_t *lock_task_rq(task_t *p, unsigned long *flags)
+static inline runqueue_t *task_rq_lock(task_t *p, unsigned long *flags)
 {
-	struct runqueue *__rq;
+	struct runqueue *rq;
 
 repeat_lock_task:
 	preempt_disable();
-	__rq = task_rq(p);
-	spin_lock_irqsave(&__rq->lock, *flags);
-	if (unlikely(__rq != task_rq(p))) {
-		spin_unlock_irqrestore(&__rq->lock, *flags);
+	rq = task_rq(p);
+	spin_lock_irqsave(&rq->lock, *flags);
+	if (unlikely(rq != task_rq(p))) {
+		spin_unlock_irqrestore(&rq->lock, *flags);
 		preempt_enable();
 		goto repeat_lock_task;
 	}
-	return __rq;
+	return rq;
 }
 
-static inline void unlock_task_rq(runqueue_t *rq, unsigned long *flags)
+static inline void task_rq_unlock(runqueue_t *rq, unsigned long *flags)
 {
 	spin_unlock_irqrestore(&rq->lock, *flags);
 	preempt_enable();
@@ -184,7 +184,7 @@ static inline void unlock_task_rq(runqueue_t *rq, unsigned long *flags)
 static inline void dequeue_task(struct task_struct *p, prio_array_t *array)
 {
 	array->nr_active--;
-	list_del_init(&p->run_list);
+	list_del(&p->run_list);
 	if (list_empty(array->queue + p->prio))
 		__clear_bit(p->prio, array->bitmap);
 }
@@ -289,30 +289,16 @@ void wait_task_inactive(task_t * p)
 		cpu_relax();
 		barrier();
 	}
-	rq = lock_task_rq(p, &flags);
+	rq = task_rq_lock(p, &flags);
 	if (unlikely(rq->curr == p)) {
-		unlock_task_rq(rq, &flags);
+		task_rq_unlock(rq, &flags);
 		preempt_enable();
 		goto repeat;
 	}
-	unlock_task_rq(rq, &flags);
+	task_rq_unlock(rq, &flags);
 	preempt_enable();
 }
 
-/*
- * The SMP message passing code calls this function whenever
- * the new task has arrived at the target CPU. We move the
- * new task into the local runqueue.
- *
- * This function must be called with interrupts disabled.
- */
-void sched_task_migrated(task_t *new_task)
-{
-	wait_task_inactive(new_task);
-	new_task->thread_info->cpu = smp_processor_id();
-	wake_up_process(new_task);
-}
-
 /*
  * Kick the remote CPU if the task is running currently,
  * this code is used by the signal code to signal tasks
@@ -337,27 +323,27 @@ void kick_if_running(task_t * p)
  * "current->state = TASK_RUNNING" to mark yourself runnable
  * without the overhead of this.
  */
-static int try_to_wake_up(task_t * p, int synchronous)
+static int try_to_wake_up(task_t * p)
 {
 	unsigned long flags;
 	int success = 0;
 	runqueue_t *rq;
 
-	rq = lock_task_rq(p, &flags);
+	rq = task_rq_lock(p, &flags);
 	p->state = TASK_RUNNING;
 	if (!p->array) {
 		activate_task(p, rq);
-		if ((rq->curr == rq->idle) || (p->prio < rq->curr->prio))
+		if (p->prio < rq->curr->prio)
 			resched_task(rq->curr);
 		success = 1;
 	}
-	unlock_task_rq(rq, &flags);
+	task_rq_unlock(rq, &flags);
 	return success;
 }
 
 int wake_up_process(task_t * p)
 {
-	return try_to_wake_up(p, 0);
+	return try_to_wake_up(p);
 }
 
 void wake_up_forked_process(task_t * p)
@@ -366,6 +352,7 @@ void wake_up_forked_process(task_t * p)
 
 	preempt_disable();
 	rq = this_rq();
+	spin_lock_irq(&rq->lock);
 
 	p->state = TASK_RUNNING;
 	if (!rt_task(p)) {
@@ -378,10 +365,12 @@ void wake_up_forked_process(task_t * p)
 		p->sleep_avg = p->sleep_avg * CHILD_PENALTY / 100;
 		p->prio = effective_prio(p);
 	}
-	spin_lock_irq(&rq->lock);
+	INIT_LIST_HEAD(&p->migration_list);
 	p->thread_info->cpu = smp_processor_id();
 	activate_task(p, rq);
+
 	spin_unlock_irq(&rq->lock);
+	init_MUTEX(&p->migration_sem);
 	preempt_enable();
 }
 
@@ -861,44 +850,33 @@ asmlinkage void preempt_schedule(void)
  * started to run but is not in state TASK_RUNNING.  try_to_wake_up() returns
  * zero in this (rare) case, and we handle it by continuing to scan the queue.
  */
-static inline void __wake_up_common (wait_queue_head_t *q, unsigned int mode,
-			 	     int nr_exclusive, const int sync)
+static inline void __wake_up_common(wait_queue_head_t *q, unsigned int mode, int nr_exclusive)
 {
 	struct list_head *tmp;
+	unsigned int state;
+	wait_queue_t *curr;
 	task_t *p;
 
-	list_for_each(tmp,&q->task_list) {
-		unsigned int state;
-		wait_queue_t *curr = list_entry(tmp, wait_queue_t, task_list);
-
+	list_for_each(tmp, &q->task_list) {
+		curr = list_entry(tmp, wait_queue_t, task_list);
 		p = curr->task;
 		state = p->state;
-		if ((state & mode) &&
-				try_to_wake_up(p, sync) &&
-				((curr->flags & WQ_FLAG_EXCLUSIVE) &&
-					!--nr_exclusive))
-			break;
+		if ((state & mode) && try_to_wake_up(p) &&
+			((curr->flags & WQ_FLAG_EXCLUSIVE) && !--nr_exclusive))
+				break;
 	}
 }
 
-void __wake_up(wait_queue_head_t *q, unsigned int mode, int nr)
+void __wake_up(wait_queue_head_t *q, unsigned int mode, int nr_exclusive)
 {
-	if (q) {
-		unsigned long flags;
-		wq_read_lock_irqsave(&q->lock, flags);
-		__wake_up_common(q, mode, nr, 0);
-		wq_read_unlock_irqrestore(&q->lock, flags);
-	}
-}
+	unsigned long flags;
 
-void __wake_up_sync(wait_queue_head_t *q, unsigned int mode, int nr)
-{
-	if (q) {
-		unsigned long flags;
-		wq_read_lock_irqsave(&q->lock, flags);
-		__wake_up_common(q, mode, nr, 1);
-		wq_read_unlock_irqrestore(&q->lock, flags);
-	}
+	if (unlikely(!q))
+		return;
+
+	wq_read_lock_irqsave(&q->lock, flags);
+	__wake_up_common(q, mode, nr_exclusive);
+	wq_read_unlock_irqrestore(&q->lock, flags);
 }
 
 void complete(struct completion *x)
@@ -907,7 +885,7 @@ void complete(struct completion *x)
 
 	spin_lock_irqsave(&x->wait.lock, flags);
 	x->done++;
-	__wake_up_common(&x->wait, TASK_UNINTERRUPTIBLE | TASK_INTERRUPTIBLE, 1, 0);
+	__wake_up_common(&x->wait, TASK_UNINTERRUPTIBLE | TASK_INTERRUPTIBLE, 1);
 	spin_unlock_irqrestore(&x->wait.lock, flags);
 }
 
@@ -994,35 +972,66 @@ long sleep_on_timeout(wait_queue_head_t *q, long timeout)
 	return timeout;
 }
 
+void scheduling_functions_end_here(void) { }
+
+#if CONFIG_SMP
+
 /*
- * Change the current task's CPU affinity. Migrate the process to a
- * proper CPU and schedule away if the current CPU is removed from
- * the allowed bitmask.
+ * Change a given task's CPU affinity. Migrate the process to a
+ * proper CPU and schedule it away if the current CPU is removed
+ * from the allowed bitmask.
  */
 void set_cpus_allowed(task_t *p, unsigned long new_mask)
 {
+	unsigned long flags;
+	runqueue_t *rq;
+	int dest_cpu;
+
+	down(&p->migration_sem);
+	if (!list_empty(&p->migration_list))
+		BUG();
+
 	new_mask &= cpu_online_map;
 	if (!new_mask)
 		BUG();
-	if (p != current)
-		BUG();
 
+	rq = task_rq_lock(p, &flags);
 	p->cpus_allowed = new_mask;
 	/*
-	 * Can the task run on the current CPU? If not then
+	 * Can the task run on the task's current CPU? If not then
 	 * migrate the process off to a proper CPU.
 	 */
-	if (new_mask & (1UL << smp_processor_id()))
-		return;
-#if CONFIG_SMP
-	current->state = TASK_UNINTERRUPTIBLE;
-	smp_migrate_task(__ffs(new_mask), current);
+	if (new_mask & (1UL << p->thread_info->cpu)) {
+		task_rq_unlock(rq, &flags);
+		goto out;
+	}
+	/*
+	 * We mark the process as nonrunnable, and kick it to
+	 * schedule away from its current CPU. We also add
+	 * the task to the migration queue and wake up the
+	 * target CPU's migration thread, so that it can pick
+	 * up this task and insert it into the local runqueue.
+	 */
+	p->state = TASK_UNINTERRUPTIBLE;
+	kick_if_running(p);
+	task_rq_unlock(rq, &flags);
 
-	schedule();
-#endif
+	dest_cpu = __ffs(new_mask);
+	rq = cpu_rq(dest_cpu);
+
+	spin_lock_irq(&rq->lock);
+	list_add(&p->migration_list, &rq->migration_queue);
+	spin_unlock_irq(&rq->lock);
+	wake_up_process(rq->migration_thread);
+
+	while (!((1UL << p->thread_info->cpu) & p->cpus_allowed) &&
+			(p->state != TASK_ZOMBIE))
+		yield();
+out:
+	up(&p->migration_sem);
 }
 
-void scheduling_functions_end_here(void) { }
+#endif
 
 void set_user_nice(task_t *p, long nice)
 {
@@ -1036,7 +1045,7 @@ void set_user_nice(task_t *p, long nice)
 	 * We have to be careful, if called from sys_setpriority(),
 	 * the task might be in the middle of scheduling on another CPU.
 	 */
-	rq = lock_task_rq(p, &flags);
+	rq = task_rq_lock(p, &flags);
 	if (rt_task(p)) {
 		p->static_prio = NICE_TO_PRIO(nice);
 		goto out_unlock;
@@ -1056,7 +1065,7 @@ void set_user_nice(task_t *p, long nice)
 			resched_task(rq->curr);
 	}
 out_unlock:
-	unlock_task_rq(rq, &flags);
+	task_rq_unlock(rq, &flags);
 }
 
 #ifndef __alpha__
@@ -1154,7 +1163,7 @@ static int setscheduler(pid_t pid, int policy, struct sched_param *param)
 	 * To be able to change p->policy safely, the apropriate
 	 * runqueue lock must be held.
 	 */
-	rq = lock_task_rq(p, &flags);
+	rq = task_rq_lock(p, &flags);
 
 	if (policy < 0)
 		policy = p->policy;
@@ -1197,7 +1206,7 @@ static int setscheduler(pid_t pid, int policy, struct sched_param *param)
 		activate_task(p, task_rq(p));
 
 out_unlock:
-	unlock_task_rq(rq, &flags);
+	task_rq_unlock(rq, &flags);
 out_unlock_tasklist:
 	read_unlock_irq(&tasklist_lock);
 
@@ -1477,7 +1486,7 @@ static inline void double_rq_unlock(runqueue_t *rq1, runqueue_t *rq2)
 
 void __init init_idle(task_t *idle, int cpu)
 {
-	runqueue_t *idle_rq = cpu_rq(cpu), *rq = idle->array->rq;
+	runqueue_t *idle_rq = cpu_rq(cpu), *rq = cpu_rq(idle->thread_info->cpu);
 	unsigned long flags;
 
 	__save_flags(flags);
@@ -1509,14 +1518,13 @@ void __init sched_init(void)
 		runqueue_t *rq = cpu_rq(i);
 		prio_array_t *array;
 
-		rq->active = rq->arrays + 0;
+		rq->active = rq->arrays;
 		rq->expired = rq->arrays + 1;
 		spin_lock_init(&rq->lock);
+		INIT_LIST_HEAD(&rq->migration_queue);
 
 		for (j = 0; j < 2; j++) {
 			array = rq->arrays + j;
-			array->rq = rq;
-			array->lock = &rq->lock;
 			for (k = 0; k < MAX_PRIO; k++) {
 				INIT_LIST_HEAD(array->queue + k);
 				__clear_bit(k, array->bitmap);
@@ -1545,3 +1553,104 @@ void __init sched_init(void)
 	atomic_inc(&init_mm.mm_count);
 	enter_lazy_tlb(&init_mm, current, smp_processor_id());
 }
+
+#if CONFIG_SMP
+
+static volatile unsigned long migration_mask;
+
+static int migration_thread(void * unused)
+{
+	runqueue_t *rq;
+
+	daemonize();
+	sigfillset(&current->blocked);
+	set_user_nice(current, -20);
+
+	/*
+	 * We have to migrate manually - there is no migration thread
+	 * to do this for us yet :-)
+	 *
+	 * We use the following property of the Linux scheduler. At
+	 * this point no other task is running, so by keeping all
+	 * migration threads running, the load-balancer will distribute
+	 * them between all CPUs equally. At that point every migration
+	 * task binds itself to the current CPU.
+	 */
+
+	/* wait for all migration threads to start up. */
+	while (!migration_mask)
+		yield();
+
+	for (;;) {
+		preempt_disable();
+		if (test_and_clear_bit(smp_processor_id(), &migration_mask))
+			current->cpus_allowed = 1 << smp_processor_id();
+		if (test_thread_flag(TIF_NEED_RESCHED))
+			schedule();
+		if (!migration_mask)
+			break;
+		preempt_enable();
+	}
+	rq = this_rq();
+	rq->migration_thread = current;
+	preempt_enable();
+
+	sprintf(current->comm, "migration_CPU%d", smp_processor_id());
+
+	for (;;) {
+		struct list_head *head;
+		unsigned long flags;
+		task_t *p = NULL;
+
+		spin_lock_irqsave(&rq->lock, flags);
+		head = &rq->migration_queue;
+		if (list_empty(head)) {
+			current->state = TASK_UNINTERRUPTIBLE;
+			spin_unlock_irqrestore(&rq->lock, flags);
+			schedule();
+			continue;
+		}
+		p = list_entry(head->next, task_t, migration_list);
+		list_del_init(head->next);
+		spin_unlock_irqrestore(&rq->lock, flags);
+
+		for (;;) {
+			runqueue_t *rq2 = task_rq_lock(p, &flags);
+
+			if (!p->array) {
+				p->thread_info->cpu = smp_processor_id();
+				task_rq_unlock(rq2, &flags);
+				wake_up_process(p);
+				break;
+			}
+			if (p->state != TASK_UNINTERRUPTIBLE) {
+				p->state = TASK_UNINTERRUPTIBLE;
+				kick_if_running(p);
+			}
+			task_rq_unlock(rq2, &flags);
+			while ((p->state == TASK_UNINTERRUPTIBLE) && p->array) {
+				cpu_relax();
+				barrier();
+			}
+		}
+	}
+}
+
+void __init migration_init(void)
+{
+	int cpu;
+
+	for (cpu = 0; cpu < smp_num_cpus; cpu++)
+		if (kernel_thread(migration_thread, NULL,
+				CLONE_FS | CLONE_FILES | CLONE_SIGNAL) < 0)
+			BUG();
+
+	migration_mask = (1 << smp_num_cpus) -1;
+
+	for (cpu = 0; cpu < smp_num_cpus; cpu++)
+		while (!cpu_rq(cpu)->migration_thread)
+			yield();
+	if (migration_mask)
+		BUG();
+}
+#endif