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SubjectRe: [PATCH 1/2] sched: remove extraneous load manipulations
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On Thu, 2008-07-03 at 15:37 -0600, Gregory Haskins wrote:
> commit 62fb185130e4d420f71a30ff59d8b16b74ef5d2b reverted some patches
> in the scheduler, but it looks like it may have left a few redundant
> calls to inc_load/dec_load remain in set_user_nice (since the
> dequeue_task/enqueue_task take care of the load. This could result
> in the load values being off since the load may change while dequeued.

I just checked out v2.6.25.10 but cannot see dequeue_task() do it.

deactivate_task() otoh does do it.

static void dequeue_task(struct rq *rq, struct task_struct *p, int sleep)
{
p->sched_class->dequeue_task(rq, p, sleep);
p->se.on_rq = 0;
}
vs

static void deactivate_task(struct rq *rq, struct task_struct *p, int sleep)
{
if (task_contributes_to_load(p))
rq->nr_uninterruptible++;
dequeue_task(rq, p, sleep);
dec_nr_running(p, rq);
}
where

static void dec_nr_running(struct task_struct *p, struct rq *rq)
{
rq->nr_running--;
dec_load(rq, p);
}
And since set_user_nice() actually changes the load we'd better not
forget to do this dec/inc load stuff.

So I'm thinking this patch would actually break stuff.

> Signed-off-by: Gregory Haskins <ghaskins@novell.com>
> CC: Peter Zijlstra <peterz@infradead.org>
> CC: Ingo Molnar <mingo@elte.hu>
> ---
>
> kernel/sched.c | 6 ++----
> 1 files changed, 2 insertions(+), 4 deletions(-)
>
> diff --git a/kernel/sched.c b/kernel/sched.c
> index 31f91d9..b046754 100644
> --- a/kernel/sched.c
> +++ b/kernel/sched.c
> @@ -4679,10 +4679,8 @@ void set_user_nice(struct task_struct *p, long nice)
> goto out_unlock;
> }
> on_rq = p->se.on_rq;
> - if (on_rq) {
> + if (on_rq)
> dequeue_task(rq, p, 0);
> - dec_load(rq, p);
> - }
>
> p->static_prio = NICE_TO_PRIO(nice);
> set_load_weight(p);
> @@ -4692,7 +4690,7 @@ void set_user_nice(struct task_struct *p, long nice)
>
> if (on_rq) {
> enqueue_task(rq, p, 0);
> - inc_load(rq, p);
> +
> /*
> * If the task increased its priority or is running and
> * lowered its priority, then reschedule its CPU:
>



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