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Commit 4d78e7b6 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
Browse files

sched: new task placement for vruntime 



add proper new task placement for the vruntime based math too.

( note: introduces a swap() macro, but the swap token is too
  widely used in the kernel namespace for a generic version
  to be added without changing non-scheduler code - so this
  cleanup will be done separately. )

Signed-off-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
Signed-off-by: default avatarMike Galbraith <efault@gmx.de>
Reviewed-by: default avatarThomas Gleixner <tglx@linutronix.de>
parent 6cb58195

kernel/sched_fair.c

+27 −9
Original line number Diff line number Diff line
@@ -203,6 +203,20 @@ static struct sched_entity *__pick_next_entity(struct cfs_rq *cfs_rq) 
 * Scheduling class statistics methods:

 */



static u64 __sched_period(unsigned long nr_running)

{

	u64 period = sysctl_sched_latency;

	unsigned long nr_latency =

		sysctl_sched_latency / sysctl_sched_min_granularity;



	if (unlikely(nr_running > nr_latency)) {

		period *= nr_running;

		do_div(period, nr_latency);

	}



	return period;

}



/*

 * Calculate the preemption granularity needed to schedule every

 * runnable task once per sysctl_sched_latency amount of time.
@@ -1103,6 +1117,8 @@ static void task_tick_fair(struct rq *rq, struct task_struct *curr) 
	}

}



#define swap(a,b) do { typeof(a) tmp = (a); (a) = (b); (b) = tmp; } while (0)



/*

 * Share the fairness runtime between parent and child, thus the

 * total amount of pressure for CPU stays equal - new tasks
@@ -1118,14 +1134,9 @@ static void task_new_fair(struct rq *rq, struct task_struct *p) 
	sched_info_queued(p);



	update_curr(cfs_rq);

	se->vruntime = cfs_rq->min_vruntime;

	update_stats_enqueue(cfs_rq, se);

	/*

	 * Child runs first: we let it run before the parent

	 * until it reschedules once. We set up the key so that

	 * it will preempt the parent:

	 */

	se->fair_key = curr->fair_key -

		niced_granularity(curr, sched_granularity(cfs_rq)) - 1;



	/*

	 * The first wait is dominated by the child-runs-first logic,

	 * so do not credit it with that waiting time yet:
@@ -1138,9 +1149,16 @@ static void task_new_fair(struct rq *rq, struct task_struct *p) 
	 * -granularity/2, so initialize the task with that:

	 */

	if (sched_feat(START_DEBIT))

		se->wait_runtime = -(sched_granularity(cfs_rq) / 2);

		se->wait_runtime = -(__sched_period(cfs_rq->nr_running+1) / 2);



	if (sysctl_sched_child_runs_first &&

			curr->vruntime < se->vruntime) {



		dequeue_entity(cfs_rq, curr, 0);

		swap(curr->vruntime, se->vruntime);

		enqueue_entity(cfs_rq, curr, 0);

	}



	se->vruntime = cfs_rq->min_vruntime;

	update_stats_enqueue(cfs_rq, se);

	__enqueue_entity(cfs_rq, se);

	resched_task(rq->curr);