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    SubjectRe: [tip:core/futexes] futex: use current->time_slack_ns for rt tasks too
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    On Thu, 2009-03-12 at 06:53 -0700, Arjan van de Ven wrote:
    > Darren Hart wrote:
    > > Commit-ID: 16f4993f4e9860715918efd4eeac928f8de1218b
    > > Gitweb: http://git.kernel.org/tip/16f4993f4e9860715918efd4eeac928f8de1218b
    > > Author: "Darren Hart" <dvhltc@us.ibm.com>
    > > AuthorDate: Thu, 12 Mar 2009 00:55:59 -0700
    > > Commit: Ingo Molnar <mingo@elte.hu>
    > > CommitDate: Thu, 12 Mar 2009 11:20:57 +0100
    > >
    > > futex: use current->time_slack_ns for rt tasks too
    > >
    > > RT tasks should set their timer slack to 0 on their own. This
    > > patch removes the 'if (rt_task()) slack = 0;' block in
    > > futex_wait.
    >
    > Hi,
    >
    > can you explain the rationale for this reasoning?

    Yeah, I found it iffy as well, I think we want something like the below
    instead though..

    ---

    Subject: sched: adjust timer_slack_ns on scheduler policy change
    From: Peter Zijlstra <a.p.zijlstra@chello.nl>
    Date: Thu Mar 12 15:01:02 CET 2009

    Ensure RT tasks have 0 timer slack.

    Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
    ---
    kernel/sched.c | 2 ++
    1 file changed, 2 insertions(+)

    Index: linux-2.6/kernel/sched.c
    ===================================================================
    --- linux-2.6.orig/kernel/sched.c
    +++ linux-2.6/kernel/sched.c
    @@ -5511,10 +5511,12 @@ __setscheduler(struct rq *rq, struct tas
    case SCHED_NORMAL:
    case SCHED_BATCH:
    case SCHED_IDLE:
    + p->timer_slack_ns = p->default_timer_slack_ns;
    p->sched_class = &fair_sched_class;
    break;
    case SCHED_FIFO:
    case SCHED_RR:
    + p->timer_slack_ns = 0;
    p->sched_class = &rt_sched_class;
    break;
    }


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