2008-08-28 09:15:26

by Bharata B Rao

Subject: [patch] sched: call resched_task() conditionally from new task wake up path.

Hi,

sched: call resched_task() conditionally from new task wake up path.

- During wake up of a new task, task_new_fair() can do a resched_task()
on the current task. Later in the code path, check_preempt_curr() also ends
up doing the same, which can be avoided. Check if TIF_NEED_RESCHED is
already set for the current task.

- task_new_fair() does a resched_task() on the current task unconditionally.
This can be done only in case when child runs before the parent.

Signed-off-by: Bharata B Rao <[email protected]>
CC: Srivatsa Vaddagiri <[email protected]>
CC: Peter Zijlstra <[email protected]>
CC: Ingo Molnar <[email protected]>
---
kernel/sched_fair.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)

--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -1348,6 +1348,13 @@ static void check_preempt_wakeup(struct
if (unlikely(se == pse))
return;

+ /*
+ * We can come here with TIF_NEED_RESCHED already set from new task
+ * wake up path.
+ */
+ if (test_tsk_need_resched(curr))
+ return;
+
cfs_rq_of(pse)->next = pse;

/*
@@ -1615,10 +1622,10 @@ static void task_new_fair(struct rq *rq,
* 'current' within the tree based on its new key value.
*/
swap(curr->vruntime, se->vruntime);
+ resched_task(rq->curr);
}

enqueue_task_fair(rq, p, 0);
- resched_task(rq->curr);
}

/*

Regards,
Bharata.

2008-08-28 09:26:38

by Ingo Molnar

Subject: Re: [patch] sched: call resched_task() conditionally from new task wake up path.

* Bharata B Rao <[email protected]> wrote:

> Hi,
>
> sched: call resched_task() conditionally from new task wake up path.
>
> - During wake up of a new task, task_new_fair() can do a resched_task()
> on the current task. Later in the code path, check_preempt_curr() also ends
> up doing the same, which can be avoided. Check if TIF_NEED_RESCHED is
> already set for the current task.
>
> - task_new_fair() does a resched_task() on the current task unconditionally.
> This can be done only in case when child runs before the parent.
>
> Signed-off-by: Bharata B Rao <[email protected]>

well spotted - applied to tip/sched/devel, thanks Bharata.

Ingo

2008-08-28 09:26:53

by Peter Zijlstra

Subject: Re: [patch] sched: call resched_task() conditionally from new task wake up path.

On Thu, 2008-08-28 at 14:42 +0530, Bharata B Rao wrote:
> Hi,
>
> sched: call resched_task() conditionally from new task wake up path.
>
> - During wake up of a new task, task_new_fair() can do a resched_task()
> on the current task. Later in the code path, check_preempt_curr() also ends
> up doing the same, which can be avoided. Check if TIF_NEED_RESCHED is
> already set for the current task.
>
> - task_new_fair() does a resched_task() on the current task unconditionally.
> This can be done only in case when child runs before the parent.
>
> Signed-off-by: Bharata B Rao <[email protected]>
> CC: Srivatsa Vaddagiri <[email protected]>

Acked-by: Peter Zijlstra <[email protected]>

> CC: Ingo Molnar <[email protected]>
> ---
> kernel/sched_fair.c | 9 ++++++++-
> 1 file changed, 8 insertions(+), 1 deletion(-)
>
> --- a/kernel/sched_fair.c
> +++ b/kernel/sched_fair.c
> @@ -1348,6 +1348,13 @@ static void check_preempt_wakeup(struct
> if (unlikely(se == pse))
> return;
>
> + /*
> + * We can come here with TIF_NEED_RESCHED already set from new task
> + * wake up path.
> + */
> + if (test_tsk_need_resched(curr))
> + return;
> +
> cfs_rq_of(pse)->next = pse;
>
> /*
> @@ -1615,10 +1622,10 @@ static void task_new_fair(struct rq *rq,
> * 'current' within the tree based on its new key value.
> */
> swap(curr->vruntime, se->vruntime);
> + resched_task(rq->curr);
> }
>
> enqueue_task_fair(rq, p, 0);
> - resched_task(rq->curr);
> }
>
> /*
>
> Regards,
> Bharata.