Cset exclude: mingo@elte.hu|ChangeSet|20020416054244|19697

kernel/sched.c

@@ -1672,16 +1672,7 @@ void set_cpus_allowed(task_t *p, unsigned long new_mask)
 	preempt_enable();
 }
 
-/*
- * Treat the bits of migration_mask as lock bits.
- * If the bit corresponding to the cpu a migration_thread is
- * running on then we have failed to claim our cpu and must
- * yield in order to find another.
- */
 static volatile unsigned long migration_mask;
-static atomic_t migration_threads_seeking_cpu;
-static struct completion migration_complete
-			= COMPLETION_INITIALIZER(migration_complete);
 
 static int migration_thread(void * unused)
 {
@@ -1705,54 +1696,26 @@ static int migration_thread(void * unused)
 	 * task binds itself to the current CPU.
 	 */
 
-	preempt_disable();
-
-	/*
-	 * Enter the loop with preemption disabled so that
-	 * smp_processor_id() remains valid through the check. The
-	 * interior of the wait loop re-enables preemption in an
-	 * attempt to get scheduled off the current cpu. When the
-	 * loop is exited the lock bit in migration_mask is acquired
-	 * and preemption is disabled on the way out. This way the
-	 * cpu acquired remains valid when ->cpus_allowed is set.
-	 */
-	while (test_and_set_bit(smp_processor_id(), &migration_mask)) {
-		preempt_enable();
+	/* 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();
 	}
-
-	current->cpus_allowed = 1 << smp_processor_id();
 	rq = this_rq();
 	rq->migration_thread = current;
-
-	/*
-	 * Now that we've bound ourselves to a cpu, post to
-	 * migration_threads_seeking_cpu and wait for everyone else.
-	 * Preemption should remain disabled and the cpu should remain
-	 * in busywait. Yielding the cpu will allow the livelock
-	 * where where a timing pattern causes an idle task seeking a
-	 * migration_thread to always find the unbound migration_thread 
-	 * running on the cpu's it tries to steal tasks from.
-	 */
-	atomic_dec(&migration_threads_seeking_cpu);
-	while (atomic_read(&migration_threads_seeking_cpu))
-		cpu_relax();
-
 	preempt_enable();
 
 	sprintf(current->comm, "migration_CPU%d", smp_processor_id());
 
-	/*
-	 * Everyone's found their cpu, so now wake migration_init().
-	 * Multiple wakeups are harmless; removal from the waitqueue
-	 * has locking built-in, and waking an empty queue is valid.
-	 */
-	complete(&migration_complete);
-
-	/*
-	 * Initiate the event loop.
-	 */
 	for (;;) {
 		runqueue_t *rq_src, *rq_dest;
 		struct list_head *head;
@@ -1803,31 +1766,33 @@ static int migration_thread(void * unused)
 
 void __init migration_init(void)
 {
-	unsigned long orig_cache_decay_ticks;
+	unsigned long tmp, orig_cache_decay_ticks;
 	int cpu;
 
-	atomic_set(&migration_threads_seeking_cpu, smp_num_cpus);
+	tmp = 0;
+	for (cpu = 0; cpu < smp_num_cpus; cpu++) {
+		if (kernel_thread(migration_thread, NULL,
+				CLONE_FS | CLONE_FILES | CLONE_SIGNAL) < 0)
+			BUG();
+		tmp |= (1UL << cpu_logical_map(cpu));
+	}
 
-	preempt_disable();
+	migration_mask = tmp;
 
 	orig_cache_decay_ticks = cache_decay_ticks;
 	cache_decay_ticks = 0;
 
-	for (cpu = 0; cpu < smp_num_cpus; cpu++)
-		if (kernel_thread(migration_thread, NULL,
-				CLONE_FS | CLONE_FILES | CLONE_SIGNAL) < 0)
-			BUG();
+	for (cpu = 0; cpu < smp_num_cpus; cpu++) {
+		int logical = cpu_logical_map(cpu);
 
-	/*
-	 * We cannot have missed the wakeup for the migration_thread
-	 * bound for the cpu migration_init() is running on cannot
-	 * acquire this cpu until migration_init() has yielded it by
-	 * means of wait_for_completion().
-	 */
-	wait_for_completion(&migration_complete);
+		while (!cpu_rq(logical)->migration_thread) {
+			set_current_state(TASK_INTERRUPTIBLE);
+			schedule_timeout(2);
+		}
+	}
+	if (migration_mask)
+		BUG();
 
 	cache_decay_ticks = orig_cache_decay_ticks;
-
-	preempt_enable();
 }
 #endif