[Xen-devel] Re: [PATCH] percpu data: only iterate over possible CPUs

[Rik van Riel <riel@xxxxxxxxxx>]

On Wed, 8 Feb 2006, Rik van Riel wrote:

> On Sun, 5 Feb 2006, Linux Kernel Mailing List wrote:
> 
> > [PATCH] percpu data: only iterate over possible CPUs
> 
> The sched.c bit breaks Xen, and probably also other architectures
> that have CPU hotplug.  I suspect the reason is that during early 
> bootup only the boot CPU is online, so nothing initialises the
> runqueues for CPUs that are brought up afterwards.
> 
> I suspect we can get rid of this problem quite easily by moving
> runqueue initialisation to init_idle()...

Well, it works.  This (fairly trivial) patch makes hotplug cpu
work again, by ensuring that the runqueues of a newly brought
up CPU are initialized just before they are needed.

Without this patch the "spin_lock_irqsave(&rq->lock, flags);"
in init_idle() would oops if CONFIG_DEBUG_SPINLOCK was set.

With this patch, things just work.

Signed-off-by: Rik van Riel <riel@xxxxxxxxxx>

--- linux-2.6.15.i686/kernel/sched.c.idle_init  2006-02-08 17:56:50.000000000 
-0500
+++ linux-2.6.15.i686/kernel/sched.c    2006-02-08 17:58:57.000000000 -0500
@@ -4437,6 +4437,35 @@ void __devinit init_idle(task_t *idle, i
 {
        runqueue_t *rq = cpu_rq(cpu);
        unsigned long flags;
+       prio_array_t *array;
+       int j, k;
+
+       spin_lock_init(&rq->lock);
+       rq->nr_running = 0;
+       rq->active = rq->arrays;
+       rq->expired = rq->arrays + 1;
+       rq->best_expired_prio = MAX_PRIO;
+
+#ifdef CONFIG_SMP
+       rq->sd = NULL;
+       for (j = 1; j < 3; j++)
+               rq->cpu_load[j] = 0;
+       rq->active_balance = 0;
+       rq->push_cpu = 0;
+       rq->migration_thread = NULL;
+       INIT_LIST_HEAD(&rq->migration_queue);
+#endif
+       atomic_set(&rq->nr_iowait, 0);
+
+       for (j = 0; j < 2; j++) {
+               array = rq->arrays + j;
+               for (k = 0; k < MAX_PRIO; k++) {
+                       INIT_LIST_HEAD(array->queue + k);
+                       __clear_bit(k, array->bitmap);
+               }
+               // delimiter for bitsearch
+               __set_bit(MAX_PRIO, array->bitmap);
+       }
 
        idle->sleep_avg = 0;
        idle->array = NULL;
@@ -6110,41 +6139,6 @@ int in_sched_functions(unsigned long add
 
 void __init sched_init(void)
 {
-       runqueue_t *rq;
-       int i, j, k;
-
-       for_each_cpu(i) {
-               prio_array_t *array;
-
-               rq = cpu_rq(i);
-               spin_lock_init(&rq->lock);
-               rq->nr_running = 0;
-               rq->active = rq->arrays;
-               rq->expired = rq->arrays + 1;
-               rq->best_expired_prio = MAX_PRIO;
-
-#ifdef CONFIG_SMP
-               rq->sd = NULL;
-               for (j = 1; j < 3; j++)
-                       rq->cpu_load[j] = 0;
-               rq->active_balance = 0;
-               rq->push_cpu = 0;
-               rq->migration_thread = NULL;
-               INIT_LIST_HEAD(&rq->migration_queue);
-#endif
-               atomic_set(&rq->nr_iowait, 0);
-
-               for (j = 0; j < 2; j++) {
-                       array = rq->arrays + j;
-                       for (k = 0; k < MAX_PRIO; k++) {
-                               INIT_LIST_HEAD(array->queue + k);
-                               __clear_bit(k, array->bitmap);
-                       }
-                       // delimiter for bitsearch
-                       __set_bit(MAX_PRIO, array->bitmap);
-               }
-       }
-
        /*
         * The boot idle thread does lazy MMU switching as well:
         */

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel