Re: scheduler oddity [bug?]

[Peter Zijlstra <a.p.zijlstra@chello.nl>]

On Sun, 2009-03-08 at 10:58 +0100, Mike Galbraith wrote:
> 
> The below cures it, but is only a demo hack.
> 
> diff --git a/kernel/sched.c b/kernel/sched.c
> index 8e2558c..85f9ced 100644
> --- a/kernel/sched.c
> +++ b/kernel/sched.c
> @@ -1712,11 +1712,15 @@ static void enqueue_task(struct rq *rq, struct task_struct *p, int wakeup)
>  
>  static void dequeue_task(struct rq *rq, struct task_struct *p, int sleep)
>  {
> +       u64 limit = sysctl_sched_migration_cost;
> +       u64 runtime = p->se.sum_exec_runtime - p->se.prev_sum_exec_runtime;
> +
>         if (sleep && p->se.last_wakeup) {
>                 update_avg(&p->se.avg_overlap,
>                            p->se.sum_exec_runtime - p->se.last_wakeup);
>                 p->se.last_wakeup = 0;
> -       }


Wouldn't something like the below be more suited:

diff --git a/kernel/sched.c b/kernel/sched.c
index 89e2ca0..94c8b02 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -2501,7 +2501,7 @@ static void __sched_fork(struct task_struct *p)
 	p->se.prev_sum_exec_runtime	= 0;
 	p->se.nr_migrations		= 0;
 	p->se.last_wakeup		= 0;
-	p->se.avg_overlap		= 0;
+	p->se.avg_overlap		= sysctl_sched_migration_cost;
 	p->se.start_runtime		= 0;
 	p->se.avg_wakeup		= sysctl_sched_wakeup_granularity;