[PATCH v2 3/7] sched: Teach arch_asym_cpu_priority() the idle state of SMT siblings

[Ricardo Neri]

Some processors (e.g., Intel processors with ITMT) use asym_packing to
balance load between physical cores with SMT. In such case, a core with all
its SMT siblings idle is more desirable than another with one or more busy
siblings.

Other processors (e.g, Power7 with SMT8) use asym_packing to balance load
among SMT siblings of different priority, regardless of their idle state.

Add a new parameter, check_smt, that architectures can use as needed.

Cc: Ben Segall <bsegall@xxxxxxxxxx>
Cc: Daniel Bristot de Oliveira <bristot@xxxxxxxxxx>
Cc: Dietmar Eggemann <dietmar.eggemann@xxxxxxx>
Cc: Len Brown <len.brown@xxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxx>
Cc: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
Cc: Srinivas Pandruvada <srinivas.pandruvada@xxxxxxxxxxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: Tim C. Chen <tim.c.chen@xxxxxxxxx>
Cc: Valentin Schneider <vschneid@xxxxxxxxxx>
Cc: x86@xxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
Suggested-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Signed-off-by: Ricardo Neri <ricardo.neri-calderon@xxxxxxxxxxxxxxx>
---
Changes since v1:
 * Introduced this patch.
---
 arch/x86/kernel/itmt.c         | 2 +-
 include/linux/sched/topology.h | 2 +-
 kernel/sched/fair.c            | 5 ++++-
 kernel/sched/sched.h           | 3 ++-
 4 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kernel/itmt.c b/arch/x86/kernel/itmt.c
index 9ff480e94511..4cb5a5e4fa47 100644
--- a/arch/x86/kernel/itmt.c
+++ b/arch/x86/kernel/itmt.c
@@ -167,7 +167,7 @@ void sched_clear_itmt_support(void)
 	mutex_unlock(&itmt_update_mutex);
 }
 
-int arch_asym_cpu_priority(int cpu)
+int arch_asym_cpu_priority(int cpu, bool check_smt)
 {
 	return per_cpu(sched_core_priority, cpu);
 }
diff --git a/include/linux/sched/topology.h b/include/linux/sched/topology.h
index 816df6cc444e..87b64b9776f6 100644
--- a/include/linux/sched/topology.h
+++ b/include/linux/sched/topology.h
@@ -63,7 +63,7 @@ static inline int cpu_numa_flags(void)
 }
 #endif
 
-extern int arch_asym_cpu_priority(int cpu);
+extern int arch_asym_cpu_priority(int cpu, bool check_smt);
 
 struct sched_domain_attr {
 	int relax_domain_level;
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index d18947a9c03e..0e4251f83807 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -142,8 +142,11 @@ __setup("sched_thermal_decay_shift=", setup_sched_thermal_decay_shift);
 #ifdef CONFIG_SMP
 /*
  * For asym packing, by default the lower numbered CPU has higher priority.
+ *
+ * When doing ASYM_PACKING at the "MC" or higher domains, architectures may
+ * want to check the idle state of the SMT siblngs of @cpu.
  */
-int __weak arch_asym_cpu_priority(int cpu)
+int __weak arch_asym_cpu_priority(int cpu, bool check_smt)
 {
 	return -cpu;
 }
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 0fc7c0130755..e5e52c2e82de 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -802,7 +802,8 @@ static inline long se_weight(struct sched_entity *se)
  */
 static inline bool sched_asym_prefer(int a, int b, bool check_smt)
 {
-	return arch_asym_cpu_priority(a) > arch_asym_cpu_priority(b);
+	return arch_asym_cpu_priority(a, check_smt) >
+	       arch_asym_cpu_priority(b, check_smt);
 }
 
 struct perf_domain {
-- 
2.25.1