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SubjectRe: [patch] sched: call resched_task() conditionally from new task wake up path.
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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 <bharata@linux.vnet.ibm.com>
> CC: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>

Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>

> CC: Ingo Molnar <mingo@elte.hu>
> ---
> 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.



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