Re: [PATCH 1/2] sched: fix RT task-wakeup logic

Gregory Haskins
2008-04-24T11:55:53Z

>>> 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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