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SubjectRe: [PATCH v3 08/13] sched: Store maximum per-cpu capacity in root domain
On 1 August 2016 at 20:53, Dietmar Eggemann <dietmar.eggemann@arm.com> wrote:
> On 25/07/16 14:34, Morten Rasmussen wrote:
>
> [...]
>
>> @@ -6923,11 +6924,22 @@ static int build_sched_domains(const struct cpumask *cpu_map,
>> /* Attach the domains */
>> rcu_read_lock();
>> for_each_cpu(i, cpu_map) {
>> + rq = cpu_rq(i);
>> sd = *per_cpu_ptr(d.sd, i);
>> +
>> + /* Use READ_ONCE/WRITE_ONCE to avoid load/store tearing */
>> + if (rq->cpu_capacity_orig > READ_ONCE(rq->rd->max_cpu_capacity))
>> + WRITE_ONCE(rq->rd->max_cpu_capacity, rq->cpu_capacity_orig);
>
> We have to use d.rd rather rq->rd here since from v3 on we have this if
> condition in front of the cpu_attach_domain() call which replaces
> rq->rd with d.rd. Fixed patch below.
>
>> +
>> cpu_attach_domain(sd, d.rd, i);
>> }
>> rcu_read_unlock();
>>
>> + if (rq) {
>> + pr_info("span: %*pbl (max cpu_capacity = %lu)\n",
>> + cpumask_pr_args(cpu_map), rq->rd->max_cpu_capacity);
>> + }
>> +
>> ret = 0;
>> error:
>> __free_domain_allocs(&d, alloc_state, cpu_map);
>
> [...]
>
> -- >8 --
>
> From: Dietmar Eggemann <dietmar.eggemann@arm.com>
>
> To be able to compare the capacity of the target cpu with the highest
> available cpu capacity, store the maximum per-cpu capacity in the root
> domain.
>
> The max per-cpu capacity should be 1024 for all systems except SMT,
> where the capacity is currently based on smt_gain and the number of
> hardware threads and is <1024. If SMT can be brought to work with a
> per-thread capacity of 1024, this patch can be dropped and replaced by a
> hard-coded max capacity of 1024 (=SCHED_CAPACITY_SCALE).

FWIW, Acked-by: Vincent Guittot <vincent.guittot@linaro.org>

>
> cc: Ingo Molnar <mingo@redhat.com>
> cc: Peter Zijlstra <peterz@infradead.org>
>
> Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
> Signed-off-by: Morten Rasmussen <morten.rasmussen@arm.com>
> ---
> kernel/sched/core.c | 12 ++++++++++++
> kernel/sched/sched.h | 2 ++
> 2 files changed, 14 insertions(+)
>
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index a0a74b2d9f41..db03e6226d54 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -6873,6 +6873,7 @@ static int build_sched_domains(const struct cpumask *cpu_map,
> enum s_alloc alloc_state;
> struct sched_domain *sd;
> struct s_data d;
> + struct rq *rq = NULL;
> int i, ret = -ENOMEM;
>
> alloc_state = __visit_domain_allocation_hell(&d, cpu_map);
> @@ -6923,11 +6924,22 @@ static int build_sched_domains(const struct cpumask *cpu_map,
> /* Attach the domains */
> rcu_read_lock();
> for_each_cpu(i, cpu_map) {
> + rq = cpu_rq(i);
> sd = *per_cpu_ptr(d.sd, i);
> +
> + /* Use READ_ONCE/WRITE_ONCE to avoid load/store tearing */
> + if (rq->cpu_capacity_orig > READ_ONCE(d.rd->max_cpu_capacity))
> + WRITE_ONCE(d.rd->max_cpu_capacity, rq->cpu_capacity_orig);
> +
> cpu_attach_domain(sd, d.rd, i);
> }
> rcu_read_unlock();
>
> + if (rq) {
> + pr_info("span: %*pbl (max cpu_capacity = %lu)\n",
> + cpumask_pr_args(cpu_map), rq->rd->max_cpu_capacity);
> + }
> +
> ret = 0;
> error:
> __free_domain_allocs(&d, alloc_state, cpu_map);
> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> index f44da95c70cd..444d8f38743f 100644
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -565,6 +565,8 @@ struct root_domain {
> */
> cpumask_var_t rto_mask;
> struct cpupri cpupri;
> +
> + unsigned long max_cpu_capacity;
> };
>
> extern struct root_domain def_root_domain;
> --
> 1.9.1

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