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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 <bharata@linux.vnet.ibm.com>
CC: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
CC: 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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