On Mon, May 29, 2017 at 05:03:01PM -0400, Nicolas Pitre wrote:
> On most small systems where user space is tightly controlled, the realtime
> scheduling class can often be dispensed with to reduce the kernel footprint.
> Let's make it configurable.
>
> Signed-off-by: Nicolas Pitre <n...@linaro.org>
> ---
> static inline int rt_prio(int prio)
> {
> - if (unlikely(prio < MAX_RT_PRIO))
> + if (IS_ENABLED(CONFIG_SCHED_RT) && unlikely(prio < MAX_RT_PRIO))
> return 1;
> return 0;
> }
> #ifdef CONFIG_PREEMPT_NOTIFIERS
> INIT_HLIST_HEAD(&p->preempt_notifiers);
> @@ -3716,13 +3720,18 @@ void rt_mutex_setprio(struct task_struct *p, struct
> task_struct *pi_task)
> p->sched_class = &dl_sched_class;
> } else
> #endif
> +#ifdef CONFIG_SCHED_RT
> if (rt_prio(prio)) {
This ifdef is not necessary since rt_prio is conditioned on
CONFIG_SCHED_RT already.
> if (oldprio < prio)
> queue_flag |= ENQUEUE_HEAD;
> p->sched_class = &rt_sched_class;
> - } else {
> + } else
> +#endif
> + {
> +#ifdef CONFIG_SCHED_RT
> if (rt_prio(oldprio))
> p->rt.timeout = 0;
> +#endif
> p->sched_class = &fair_sched_class;
> }
>
> @@ -3997,6 +4006,23 @@ static int __sched_setscheduler(struct task_struct *p,
>
> /* May grab non-irq protected spin_locks: */
> BUG_ON(in_interrupt());
> +
> + /*
> + * When the RT scheduling class is disabled, let's make sure kernel
> threads
> + * wanting RT still get lowest nice value to give them highest available
> + * priority rather than simply returning an error. Obviously we can't
> test
> + * rt_policy() here as it is always false in that case.
> + */
> + if (!IS_ENABLED(CONFIG_SCHED_RT) && !user &&
> + (policy == SCHED_FIFO || policy == SCHED_RR)) {
> + static const struct sched_attr k_attr = {
> + .sched_policy = SCHED_NORMAL,
> + .sched_nice = MIN_NICE,
> + };
> + attr = &k_attr;
> + policy = SCHED_NORMAL;
> + }
> +
> recheck:
> /* Double check policy once rq lock held: */
> if (policy < 0) {
> @@ -5726,7 +5752,9 @@ void __init sched_init_smp(void)
> sched_init_granularity();
> free_cpumask_var(non_isolated_cpus);
>
> +#ifdef CONFIG_SCHED_RT
> init_sched_rt_class();
> +#endif
You can do an empty inline function for !CONFIG_SCHED_RT.
> #ifdef CONFIG_SCHED_DL
> init_sched_dl_class();
> #endif
And here in the earlier patch.
> @@ -5832,7 +5860,9 @@ void __init sched_init(void)
> }
> #endif /* CONFIG_CPUMASK_OFFSTACK */
>
> +#ifdef CONFIG_SCHED_RT
> init_rt_bandwidth(&def_rt_bandwidth, global_rt_period(),
> global_rt_runtime());
> +#endif
And so on...
Rob
