sched/core: Store maximum per-CPU capacity in root domain

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).

Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Signed-off-by: Morten Rasmussen <morten.rasmussen@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: freedom.tan@mediatek.com
Cc: keita.kobayashi.ym@renesas.com
Cc: mgalbraith@suse.de
Cc: sgurrappadi@nvidia.com
Cc: vincent.guittot@linaro.org
Cc: yuyang.du@intel.com
Link: http://lkml.kernel.org/r/26c69258-9947-f830-a53e-0c54e7750646@arm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 4695df6ed752d43f83318b5c69a9973d7604953d..69243142cad117f7e006c62cab0019fa11722f1d 100644 (file)
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -6903,6 +6903,7 @@ 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);
@@ -6953,11 +6954,22 @@ 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 afe76d04e916b273c69c0f2d92b8dcc4c54f95d2..420c05d099c3867dec0083249b1a860d76506feb 100644 (file)
--- 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;