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

diff --git a/kernel/sched.c b/kernel/sched.c
index 9a002953bc881fcda3c19c33fefee4b07f6e458a..d4c4996bb052e302439ff0db7e926460603a2a69 100644 (file)
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -1672,16 +1672,7 @@ out:
        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 @@ repeat:
 
 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