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Subject[PATCH v5 06/14] sched/topology: Lowest energy aware balancing sched_domain level pointer
Date
Add another member to the family of per-cpu sched_domain shortcut
pointers. This one, sd_ea, points to the lowest level at which energy
aware scheduling should be used.

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_ea shortcut is wired to the lowest
scheduling domain at which the SD_ASYM_CPUCAPACITY flag is set. For
example, it is possible to apply Energy-Aware Scheduling 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/sched.h | 1 +
kernel/sched/topology.c | 4 ++++
2 files changed, 5 insertions(+)

diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index fdf6924d53e7..25d64a0b6fe0 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1198,6 +1198,7 @@ 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_ea);

struct sched_group_capacity {
atomic_t ref;
diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
index ade1eae9d21b..8f3f746b0d5e 100644
--- a/kernel/sched/topology.c
+++ b/kernel/sched/topology.c
@@ -514,6 +514,7 @@ 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_ea);

static void update_top_cache_domain(int cpu)
{
@@ -539,6 +540,9 @@ static void update_top_cache_domain(int cpu)

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

/*
--
2.18.0
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