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

Ingo Molnar
2007-04-19T10:18:53Z

* Ingo Molnar <mingo@elte.hu> wrote:

> > I think a better approach would be to keep track of the rightmost
> > entry, set the key to the rightmost's key +1 and then simply insert
> > it there.
>
> yeah. I had that implemented at a stage but was trying to be too
> clever for my own good ;-)

i have fixed it via the patch below. (I'm using rb_last() because that
way the normal scheduling codepaths are not burdened with the
maintainance of a rightmost entry.)

Ingo

---
kernel/sched.c | 3 ++-
kernel/sched_fair.c | 24 +++++++++++++-----------
2 files changed, 15 insertions(+), 12 deletions(-)

Index: linux/kernel/sched.c
===================================================================
--- linux.orig/kernel/sched.c
+++ linux/kernel/sched.c
@@ -3806,7 +3806,8 @@ asmlinkage long sys_sched_yield(void)
schedstat_inc(rq, yld_cnt);
if (rq->nr_running == 1)
schedstat_inc(rq, yld_act_empty);
- current->sched_class->yield_task(rq, current);
+ else
+ current->sched_class->yield_task(rq, current);

/*
* Since we are going to call schedule() anyway, there's
Index: linux/kernel/sched_fair.c
===================================================================
--- linux.orig/kernel/sched_fair.c
+++ linux/kernel/sched_fair.c
@@ -275,21 +275,23 @@ static void dequeue_task_fair(struct rq
*/
static void yield_task_fair(struct rq *rq, struct task_struct *p)
{
+ struct rb_node *entry;
+ struct task_struct *last;
+
dequeue_task_fair(rq, p);
p->on_rq = 0;
+
/*
- * Temporarily insert at the last position of the tree:
+ * Temporarily insert at the last position of the tree.
+ * The key will be updated back to (near) its old value
+ * when the task gets scheduled.
*/
- p->fair_key = LLONG_MAX;
+ entry = rb_last(&rq->tasks_timeline);
+ last = rb_entry(entry, struct task_struct, run_node);
+
+ p->fair_key = last->fair_key + 1;
__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;
}

/*