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    SubjectRe: [PATCH 1/2] sched: fix RT task-wakeup logic
    >>> On Wed, Apr 23, 2008 at  7:13 AM, in message
    <20080423111329.4981.88455.stgit@novell1.haskins.net>, Gregory Haskins
    <ghaskins@novell.com> wrote:
    > Dmitry Adamushko pointed out a logic error in task_wake_up_rt() where we
    > will always evaluate to "true". You can find the thread here:
    >
    > http://lkml.org/lkml/2008/4/22/296
    >
    > In reality, we only want to try to push tasks away when a wake up request is
    > not going to preempt the current task. So lets fix it.
    >
    > Note: We introduce test_tsk_need_resched() instead of open-coding the flag
    > check so that the merge-conflict with -rt should help remind us that we
    > may need to support NEEDS_RESCHED_DELAYED in the future, too.
    >
    > Signed-off-by: Gregory Haskins <ghaskins@novell.com>
    > CC: Dmitry Adamushko <dmitry.adamushko@gmail.com>
    > CC: Ingo Molnar <mingo@elte.hu>
    > CC: Steven Rostedt <rostedt@goodmis.org>


    Hi Ingo,
    So based on the discussion and the sign-off on this patch from Dmitry and Steven, I would propose to move patch #1 from "RFC" to "Consider for inclusion" status. Patch #2 should remain RFC pending further discussion. I would recommend #1 to be considered for both 25.y stable as well as going into the 26 merge window (pending positive testing results, and your discretion).

    Regards,
    -Greg


    > ---
    >
    > include/linux/sched.h | 7 ++++++-
    > kernel/sched_rt.c | 7 +++++--
    > 2 files changed, 11 insertions(+), 3 deletions(-)
    >
    > diff --git a/include/linux/sched.h b/include/linux/sched.h
    > index 949bd54..55d4bd4 100644
    > --- a/include/linux/sched.h
    > +++ b/include/linux/sched.h
    > @@ -1966,6 +1966,11 @@ static inline void clear_tsk_need_resched(struct
    > task_struct *tsk)
    > clear_tsk_thread_flag(tsk,TIF_NEED_RESCHED);
    > }
    >
    > +static inline int test_tsk_need_resched(struct task_struct *tsk)
    > +{
    > + return unlikely(test_tsk_thread_flag(tsk,TIF_NEED_RESCHED));
    > +}
    > +
    > static inline int signal_pending(struct task_struct *p)
    > {
    > return unlikely(test_tsk_thread_flag(p,TIF_SIGPENDING));
    > @@ -1980,7 +1985,7 @@ static inline int fatal_signal_pending(struct
    > task_struct *p)
    >
    > static inline int need_resched(void)
    > {
    > - return unlikely(test_thread_flag(TIF_NEED_RESCHED));
    > + return unlikely(test_tsk_need_resched(current));
    > }
    >
    > /*
    > diff --git a/kernel/sched_rt.c b/kernel/sched_rt.c
    > index 79e5ad5..ae6b0e6 100644
    > --- a/kernel/sched_rt.c
    > +++ b/kernel/sched_rt.c
    > @@ -1058,11 +1058,14 @@ static void post_schedule_rt(struct rq *rq)
    > }
    > }
    >
    > -
    > +/*
    > + * If we are not running and we are not going to reschedule soon, we should
    > + * try to push tasks away now
    > + */
    > static void task_wake_up_rt(struct rq *rq, struct task_struct *p)
    > {
    > if (!task_running(rq, p) &&
    > - (p->prio >= rq->rt.highest_prio) &&
    > + !test_tsk_need_resched(rq->curr) &&
    > rq->rt.overloaded)
    > push_rt_tasks(rq);
    > }
    >
    > --
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