Re: CFS and suspend2: hang in atomic copy (was: [Announce] [patch] Modular Scheduler Core and Completely Fair Scheduler [CFS])

Ingo Molnar
2007-04-18T16:46:50Z

* Christian Hesse <mail@earthworm.de> wrote:

> Hi Ingo and all,
>
> On Friday 13 April 2007, Ingo Molnar wrote:
> > as usual, any sort of feedback, bugreports, fixes and suggestions are
> > more than welcome,
>
> I just gave CFS a try on my system. From a user's point of view it
> looks good so far. Thanks for your work.

you are welcome!

> However I found a problem: When trying to suspend a system patched
> with suspend2 2.2.9.11 it hangs with "doing atomic copy". Pressing the
> ESC key results in a message that it tries to abort suspend, but then
> still hangs.

i took a quick look at suspend2 and it makes some use of yield().
There's a bug in CFS's yield code, i've attached a patch that should fix
it, does it make any difference to the hang?

Ingo

Index: linux/kernel/sched_fair.c
===================================================================
--- linux.orig/kernel/sched_fair.c
+++ linux/kernel/sched_fair.c
@@ -264,15 +264,26 @@ static void dequeue_task_fair(struct rq

/*
* sched_yield() support is very simple via the rbtree, we just
- * dequeue and enqueue the task, which causes the task to
- * roundrobin to the end of the tree:
+ * dequeue the task and move it to the rightmost position, which
+ * causes the task to roundrobin to the end of the tree.
*/
static void requeue_task_fair(struct rq *rq, struct task_struct *p)
{
dequeue_task_fair(rq, p);
p->on_rq = 0;
- enqueue_task_fair(rq, p);
+ /*
+ * Temporarily insert at the last position of the tree:
+ */
+ p->fair_key = LLONG_MAX;
+ __enqueue_task_fair(rq, p);
p->on_rq = 1;
+
+ /*
+ * Update the key to the real value, so that when all other
+ * tasks from before the rightmost position have executed,
+ * this task is picked up again:
+ */
+ p->fair_key = rq->fair_clock - p->wait_runtime + p->nice_offset;
}

/*
@@ -380,7 +391,10 @@ static void task_tick_fair(struct rq *rq
* Dequeue and enqueue the task to update its
* position within the tree:
*/
- requeue_task_fair(rq, curr);
+ dequeue_task_fair(rq, curr);
+ curr->on_rq = 0;
+ enqueue_task_fair(rq, curr);
+ curr->on_rq = 1;

/*
* Reschedule if another task tops the current one.