On Sun, May 5, 2013 at 6:45 PM, Alex Shi <alex....@intel.com> wrote:
> We need initialize the se.avg.{decay_count, load_avg_contrib} for a
> new forked task.
> Otherwise random values of above variables cause mess when do new task
> enqueue:
> enqueue_task_fair
> enqueue_entity
> enqueue_entity_load_avg
>
> and make forking balancing imbalance since incorrect load_avg_contrib.
>
> set avg.decay_count = 0, and avg.load_avg_contrib = se->load.weight to
> resolve such issues.
>
> Signed-off-by: Alex Shi <alex....@intel.com>
> ---
> kernel/sched/core.c | 6 ++++++
> kernel/sched/fair.c | 4 ++++
> 2 files changed, 10 insertions(+)
>
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index c8db984..ecec7f1 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -1566,6 +1566,7 @@ static void __sched_fork(struct task_struct *p)
> #ifdef CONFIG_SMP
> p->se.avg.runnable_avg_period = 0;
> p->se.avg.runnable_avg_sum = 0;
> + p->se.avg.decay_count = 0;
> #endif
> #ifdef CONFIG_SCHEDSTATS
> memset(&p->se.statistics, 0, sizeof(p->se.statistics));
> @@ -1653,6 +1654,11 @@ void sched_fork(struct task_struct *p)
> p->sched_reset_on_fork = 0;
> }
>
> + /* New forked task assumed with full utilization */
> +#if defined(CONFIG_SMP)
> + p->se.avg.load_avg_contrib = p->se.load.weight;
This is missing a scale_load() right? Further: Why not put this in
__sched_fork?
We should also charge a minimum period to make the numbers a little
more kosher, e.g.:
+ p->se.avg.runnable_avg_period = 1024;
+ p->se.avg.runnable_avg_sum = 1024;
Rather than exposing the representation of load_avg_contrib to
__sched_fork it might also be better to call:
__update_task_entity_contrib(&p->se)
After the initialization above; this would also avoid potential bugs
like the missing scale_load() above.
> +#endif
> +
> if (!rt_prio(p->prio))
> p->sched_class = &fair_sched_class;
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 9c2f726..2881d42 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -1508,6 +1508,10 @@ static inline void enqueue_entity_load_avg(struct
> cfs_rq *cfs_rq,
> * We track migrations using entity decay_count <= 0, on a wake-up
> * migration we use a negative decay count to track the remote decays
> * accumulated while sleeping.
> + *
> + * When enqueue a new forked task, the se->avg.decay_count == 0, so
> + * we bypass update_entity_load_avg(), use avg.load_avg_contrib
> initial
> + * value: se->load.weight.
> */
> if (unlikely(se->avg.decay_count <= 0)) {
> se->avg.last_runnable_update = rq_of(cfs_rq)->clock_task;
> --
> 1.7.12
>
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