sched/topology: Lowest energy aware balancing sched_domain level pointer

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>

diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index f4d104ff0b61819bf57b1c258a37fa0d04c216fa..2484334f58db9b97fc95aeffa4761313f32ad230 100644 (file)
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1200,6 +1200,7 @@ 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 bcd40e71b05969416c4232f0df9b68a8d9b85af4..787dcae48ce875f41a8370763c685e532176cfba 100644 (file)
--- 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);
 }
 
 /*