On 08/12/15 22:19, Steve Muckle wrote:
> From: Vincent Guittot <vincent.guit...@linaro.org>
>
> RT tasks don't provide any running constraints like deadline ones
> except their running priority. The only current usable input to
> estimate the capacity needed by RT tasks is the rt_avg metric. We use
> it to estimate the CPU capacity needed for the RT scheduler class.
>
> In order to monitor the evolution for RT task load, we must
> peridiocally check it during the tick.
>
> Then, we use the estimated capacity of the last activity to estimate
> the next one which can not be that accurate but is a good starting
> point without any impact on the wake up path of RT tasks.
>
> Signed-off-by: Vincent Guittot <vincent.guit...@linaro.org>
> Signed-off-by: Steve Muckle <smuc...@linaro.org>
> ---
> kernel/sched/rt.c | 49 ++++++++++++++++++++++++++++++++++++++++++++++++-
> 1 file changed, 48 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
> index 8ec86ab..9694204 100644
> --- a/kernel/sched/rt.c
> +++ b/kernel/sched/rt.c
> @@ -1426,6 +1426,41 @@ static void check_preempt_curr_rt(struct rq *rq,
> struct task_struct *p, int flag
> #endif
> }
>
> +#ifdef CONFIG_SMP
s/SMP/CPU_FREQ_GOV_SCHED/ ?
> +static void sched_rt_update_capacity_req(struct rq *rq)
> +{
> + u64 total, used, age_stamp, avg;
> + s64 delta;
> +
> + if (!sched_freq())
> + return;
> +
> + sched_avg_update(rq);
> + /*
> + * Since we're reading these variables without serialization make sure
> + * we read them once before doing sanity checks on them.
> + */
> + age_stamp = READ_ONCE(rq->age_stamp);
> + avg = READ_ONCE(rq->rt_avg);
> + delta = rq_clock(rq) - age_stamp;
> +
> + if (unlikely(delta < 0))
> + delta = 0;
> +
> + total = sched_avg_period() + delta;
> +
> + used = div_u64(avg, total);
> + if (unlikely(used > SCHED_CAPACITY_SCALE))
> + used = SCHED_CAPACITY_SCALE;
> +
> + set_rt_cpu_capacity(rq->cpu, 1, (unsigned long)(used));
Minor nitpick: s/1/true/ .
Thanks,
- Juri
> +}
> +#else
> +static inline void sched_rt_update_capacity_req(struct rq *rq)
> +{ }
> +
> +#endif
> +
> static struct sched_rt_entity *pick_next_rt_entity(struct rq *rq,
> struct rt_rq *rt_rq)
> {
> @@ -1494,8 +1529,17 @@ pick_next_task_rt(struct rq *rq, struct task_struct
> *prev)
> if (prev->sched_class == &rt_sched_class)
> update_curr_rt(rq);
>
> - if (!rt_rq->rt_queued)
> + if (!rt_rq->rt_queued) {
> + /*
> + * The next task to be picked on this rq will have a lower
> + * priority than rt tasks so we can spend some time to update
> + * the capacity used by rt tasks based on the last activity.
> + * This value will be the used as an estimation of the next
> + * activity.
> + */
> + sched_rt_update_capacity_req(rq);
> return NULL;
> + }
>
> put_prev_task(rq, prev);
>
> @@ -2212,6 +2256,9 @@ static void task_tick_rt(struct rq *rq, struct
> task_struct *p, int queued)
>
> update_curr_rt(rq);
>
> + if (rq->rt.rt_nr_running)
> + sched_rt_update_capacity_req(rq);
> +
> watchdog(rq, p);
>
> /*
> --
> 2.4.10
>
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