Re: [RFCv5 PATCH 11/46] sched: Remove blocked load and utilization contributions of dying tasks

Leo Yan
2015-07-22T06:51:13Z

On Tue, Jul 07, 2015 at 07:23:54PM +0100, Morten Rasmussen wrote:
> Tasks being dequeued for the last time (state == TASK_DEAD) are dequeued
> with the DEQUEUE_SLEEP flag which causes their load and utilization
> contributions to be added to the runqueue blocked load and utilization.
> Hence they will contain load or utilization that is gone away. The issue
> only exists for the root cfs_rq as cgroup_exit() doesn't set
> DEQUEUE_SLEEP for task group exits.
>
> If runnable+blocked load is to be used as a better estimate for cpu
> load the dead task contributions need to be removed to prevent
> load_balance() (idle_balance() in particular) from over-estimating the
> cpu load.
>
> cc: Ingo Molnar <mingo@redhat.com>
> cc: Peter Zijlstra <peterz@infradead.org>
>
> Signed-off-by: Morten Rasmussen <morten.rasmussen@arm.com>
> ---
> kernel/sched/fair.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 775b0c7..fa12ce5 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -3217,6 +3217,8 @@ dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
> * Update run-time statistics of the 'current'.
> */
> update_curr(cfs_rq);
> + if (entity_is_task(se) && task_of(se)->state == TASK_DEAD)
> + flags &= !DEQUEUE_SLEEP;

So flags will be set to zero? Could be replaced by "flags &= ~DEQUEUE_SLEEP"?

> dequeue_entity_load_avg(cfs_rq, se, flags & DEQUEUE_SLEEP);
>
> update_stats_dequeue(cfs_rq, se);
> --
> 1.9.1
>
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