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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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