linux-kernel - [RFC PATCH v4 06/12] sched/topology: Lowest energy aware balancing sched

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Message-Id: <20180628114043.24724-7-quentin.perret@arm.com>
Date:   Thu, 28 Jun 2018 12:40:37 +0100
From:   Quentin Perret <quentin.perret@....com>
To:     peterz@...radead.org, rjw@...ysocki.net,
        linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org
Cc:     gregkh@...uxfoundation.org, mingo@...hat.com,
        dietmar.eggemann@....com, morten.rasmussen@....com,
        chris.redpath@....com, patrick.bellasi@....com,
        valentin.schneider@....com, vincent.guittot@...aro.org,
        thara.gopinath@...aro.org, viresh.kumar@...aro.org,
        tkjos@...gle.com, joel@...lfernandes.org, smuckle@...gle.com,
        adharmap@...cinc.com, skannan@...cinc.com, pkondeti@...eaurora.org,
        juri.lelli@...hat.com, edubezval@...il.com,
        srinivas.pandruvada@...ux.intel.com, currojerez@...eup.net,
        javi.merino@...nel.org, quentin.perret@....com
Subject: [RFC PATCH v4 06/12] 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@...hat.com>
cc: Peter Zijlstra <peterz@...radead.org>
Suggested-by: Morten Rasmussen <morten.rasmussen@....com>
Signed-off-by: Quentin Perret <quentin.perret@....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 7038df9fb713..1c32714aed0d 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1168,6 +1168,7 @@ 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 357eff55c1a7..368669fbf0f0 100644
--- a/kernel/sched/topology.c
+++ b/kernel/sched/topology.c
@@ -414,6 +414,7 @@ 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)
 {
@@ -439,6 +440,9 @@ 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);
 }
 
 /*
-- 
2.17.1