[PATCH v7 07/14] sched/topology: Lowest CPU asymmetry sched_domain level pointer

Quentin Perret
2018-09-12T09:13:02Z

Add another member to the family of per-cpu sched_domain shortcut
pointers. This one, sd_asym_cpucapacity, points to the lowest level
at which the SD_ASYM_CPUCAPACITY flag is set. While at it, rename the
sd_asym shortcut to sd_asym_packing to avoid confusions.

Generally speaking, the largest opportunity to save energy via
scheduling comes from a smarter exploitation of heterogeneous platforms
(i.e. big.LITTLE). Consequently, the sd_asym_cpucapacity shortcut will
be used at first as the lowest domain where Energy-Aware Scheduling
(EAS) should be applied. For example, it is possible to apply EAS within
a socket on a multi-socket system, as long as each socket has an
asymmetric topology. Cross-sockets wake-up balancing will only happen
when the system is over-utilized, or this_cpu and prev_cpu are in
different sockets.

cc: Ingo Molnar <mingo@redhat.com>
cc: Peter Zijlstra <peterz@infradead.org>
Suggested-by: Morten Rasmussen <morten.rasmussen@arm.com>
Signed-off-by: Quentin Perret <quentin.perret@arm.com>
---
kernel/sched/fair.c | 2 +-
kernel/sched/sched.h | 3 ++-
kernel/sched/topology.c | 8 ++++++--
3 files changed, 9 insertions(+), 4 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index c60616796483..c28c7adcc7b3 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -9167,7 +9167,7 @@ static void nohz_balancer_kick(struct rq *rq)
}
}

- sd = rcu_dereference(per_cpu(sd_asym, cpu));
+ sd = rcu_dereference(per_cpu(sd_asym_packing, cpu));
if (sd) {
for_each_cpu(i, sched_domain_span(sd)) {
if (i == cpu ||
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 9922615592a8..7ced27701454 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1203,7 +1203,8 @@ DECLARE_PER_CPU(int, sd_llc_size);
DECLARE_PER_CPU(int, sd_llc_id);
DECLARE_PER_CPU(struct sched_domain_shared *, sd_llc_shared);
DECLARE_PER_CPU(struct sched_domain *, sd_numa);
-DECLARE_PER_CPU(struct sched_domain *, sd_asym);
+DECLARE_PER_CPU(struct sched_domain *, sd_asym_packing);
+DECLARE_PER_CPU(struct sched_domain *, sd_asym_cpucapacity);
extern struct static_key_false sched_asym_cpucapacity;

struct sched_group_capacity {
diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
index 8019a9bf281d..10e37ffea19a 100644
--- a/kernel/sched/topology.c
+++ b/kernel/sched/topology.c
@@ -508,7 +508,8 @@ DEFINE_PER_CPU(int, sd_llc_size);
DEFINE_PER_CPU(int, sd_llc_id);
DEFINE_PER_CPU(struct sched_domain_shared *, sd_llc_shared);
DEFINE_PER_CPU(struct sched_domain *, sd_numa);
-DEFINE_PER_CPU(struct sched_domain *, sd_asym);
+DEFINE_PER_CPU(struct sched_domain *, sd_asym_packing);
+DEFINE_PER_CPU(struct sched_domain *, sd_asym_cpucapacity);
DEFINE_STATIC_KEY_FALSE(sched_asym_cpucapacity);

static void update_top_cache_domain(int cpu)
@@ -534,7 +535,10 @@ static void update_top_cache_domain(int cpu)
rcu_assign_pointer(per_cpu(sd_numa, cpu), sd);

sd = highest_flag_domain(cpu, SD_ASYM_PACKING);
- rcu_assign_pointer(per_cpu(sd_asym, cpu), sd);
+ rcu_assign_pointer(per_cpu(sd_asym_packing, cpu), sd);
+
+ sd = lowest_flag_domain(cpu, SD_ASYM_CPUCAPACITY);
+ rcu_assign_pointer(per_cpu(sd_asym_cpucapacity, cpu), sd);
}

/*
--
2.18.0