Re: [PATCH v3 2/5] sched/deadline: Add dl_bw_capacity()

Juri Lelli
2020-05-22T14:58:15Z

On 20/05/20 15:42, Dietmar Eggemann wrote:
> Capacity-aware SCHED_DEADLINE Admission Control (AC) needs root domain
> (rd) CPU capacity sum.
>
> Introduce dl_bw_capacity() which for a symmetric rd w/ a CPU capacity
> of SCHED_CAPACITY_SCALE simply relies on dl_bw_cpus() to return #CPUs
> multiplied by SCHED_CAPACITY_SCALE.
>
> For an asymmetric rd or a CPU capacity < SCHED_CAPACITY_SCALE it
> computes the CPU capacity sum over rd span and cpu_active_mask.
>
> A 'XXX Fix:' comment was added to highlight that if 'rq->rd ==
> def_root_domain' AC should be performed against the capacity of the
> CPU the task is running on rather the rd CPU capacity sum. This
> issue already exists w/o capacity awareness.
>
> Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
> ---
> kernel/sched/deadline.c | 33 +++++++++++++++++++++++++++++++++
> 1 file changed, 33 insertions(+)
>
> diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
> index 4ae22bfc37ae..ea7282ce484c 100644
> --- a/kernel/sched/deadline.c
> +++ b/kernel/sched/deadline.c
> @@ -69,6 +69,34 @@ static inline int dl_bw_cpus(int i)
>
> return cpus;
> }
> +
> +static inline unsigned long __dl_bw_capacity(int i)
> +{
> + struct root_domain *rd = cpu_rq(i)->rd;
> + unsigned long cap = 0;
> +
> + RCU_LOCKDEP_WARN(!rcu_read_lock_sched_held(),
> + "sched RCU must be held");
> +
> + for_each_cpu_and(i, rd->span, cpu_active_mask)
> + cap += capacity_orig_of(i);
> +
> + return cap;
> +}
> +
> +/*
> + * XXX Fix: If 'rq->rd == def_root_domain' perform AC against capacity
> + * of the CPU the task is running on rather rd's \Sum CPU capacity.
> + */
> +static inline unsigned long dl_bw_capacity(int i)
> +{
> + if (!static_branch_unlikely(&sched_asym_cpucapacity) &&
> + capacity_orig_of(i) == SCHED_CAPACITY_SCALE) {
> + return dl_bw_cpus(i) << SCHED_CAPACITY_SHIFT;
> + } else {
> + return __dl_bw_capacity(i);
> + }
> +}
> #else
> static inline struct dl_bw *dl_bw_of(int i)
> {
> @@ -79,6 +107,11 @@ static inline int dl_bw_cpus(int i)
> {
> return 1;
> }
> +
> +static inline unsigned long dl_bw_capacity(int i)
> +{
> + return SCHED_CAPACITY_SCALE;
> +}
> #endif
>
> static inline
> --