On 12 February 2013 14:23, Vincent Guittot <vincent.guit...@linaro.org> wrote:
> When a RT task is scheduled on an idle CPU, the update of the rq's load is
> not done because CFS's functions are not called. Then, the idle_balance,
> which is called just before entering the idle function, updates the
> rq's load and makes the assumption that the elapsed time since the last
> update, was only running time.
>
> The rq's load of a CPU that only runs a periodic RT task, is close to
> LOAD_AVG_MAX whatever the running duration of the RT task is.
>
> A new idle_exit function is called when the prev task is the idle function
> so the elapsed time will be accounted as idle time in the rq's load.
>
> Changes since V1:
> - move code out of schedule function and create a pre_schedule callback for
> idle class instead.
Hi Steve,
I have pushed a new version of my patch to have comments about the
proposed solution but I will rebase it on top of your work when
available
Vincent
>
> Signed-off-by: Vincent Guittot <vincent.guit...@linaro.org>
> ---
> kernel/sched/fair.c | 10 ++++++++++
> kernel/sched/idle_task.c | 7 +++++++
> kernel/sched/sched.h | 5 +++++
> 3 files changed, 22 insertions(+)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 81fa536..60951f1 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -1562,6 +1562,16 @@ static inline void dequeue_entity_load_avg(struct
> cfs_rq *cfs_rq,
> se->avg.decay_count = atomic64_read(&cfs_rq->decay_counter);
> } /* migrations, e.g. sleep=0 leave decay_count == 0 */
> }
> +
> +/*
> + * Update the rq's load with the elapsed idle time before a task is
> + * scheduled. if the newly scheduled task is not a CFS task, idle_exit will
> + * be the only way to update the runnable statistic.
> + */
> +void idle_exit(int this_cpu, struct rq *this_rq)
> +{
> + update_rq_runnable_avg(this_rq, 0);
> +}
> #else
> static inline void update_entity_load_avg(struct sched_entity *se,
> int update_cfs_rq) {}
> diff --git a/kernel/sched/idle_task.c b/kernel/sched/idle_task.c
> index b6baf37..27cd379 100644
> --- a/kernel/sched/idle_task.c
> +++ b/kernel/sched/idle_task.c
> @@ -13,6 +13,12 @@ select_task_rq_idle(struct task_struct *p, int sd_flag,
> int flags)
> {
> return task_cpu(p); /* IDLE tasks as never migrated */
> }
> +
> +static void pre_schedule_idle(struct rq *rq, struct task_struct *prev)
> +{
> + /* Update rq's load with elapsed idle time */
> + idle_exit(smp_processor_id(), rq);
> +}
> #endif /* CONFIG_SMP */
> /*
> * Idle tasks are unconditionally rescheduled:
> @@ -86,6 +92,7 @@ const struct sched_class idle_sched_class = {
>
> #ifdef CONFIG_SMP
> .select_task_rq = select_task_rq_idle,
> + .pre_schedule = pre_schedule_idle,
> #endif
>
> .set_curr_task = set_curr_task_idle,
> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> index fc88644..9707092 100644
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -877,6 +877,7 @@ extern const struct sched_class idle_sched_class;
>
> extern void trigger_load_balance(struct rq *rq, int cpu);
> extern void idle_balance(int this_cpu, struct rq *this_rq);
> +extern void idle_exit(int this_cpu, struct rq *this_rq);
>
> #else /* CONFIG_SMP */
>
> @@ -884,6 +885,10 @@ static inline void idle_balance(int cpu, struct rq *rq)
> {
> }
>
> +static inline void idle_exit(int this_cpu, struct rq *this_rq)
> +{
> +}
> +
> #endif
>
> extern void sysrq_sched_debug_show(void);
> --
> 1.7.9.5
>
_______________________________________________
linaro-dev mailing list
linaro-dev@lists.linaro.org
http://lists.linaro.org/mailman/listinfo/linaro-dev
