Merge "sched: Add a device tree property to specify the sched boost type"

5 files changed, 99 insertions, 6 deletions

diff --git a/Documentation/devicetree/bindings/scheduler/sched_hmp.txt b/Documentation/devicetree/bindings/scheduler/sched_hmp.txt
new file mode 100644
index 000000000000..ba1d4db9e407
--- /dev/null
+++ b/Documentation/devicetree/bindings/scheduler/sched_hmp.txt
@@ -0,0 +1,35 @@
+* HMP scheduler
+
+This file describes the bindings for an optional HMP scheduler
+node (/sched-hmp).
+
+Required properties:
+
+Optional properties:
+
+- boost-policy: The HMP scheduler has two types of task placement boost
+policies.
+
+(1) boost-on-big policy make use of all big CPUs up to their full capacity
+before using the little CPUs. This improves performance on true b.L systems
+where the big CPUs have higher efficiency compared to the little CPUs.
+
+(2) boost-on-all policy place the tasks on the CPU having the highest
+spare capacity. This policy is optimal for SMP like systems.
+
+The scheduler sets the boost policy to boost-on-big on systems which has
+CPUs of different efficiencies. However it is possible that CPUs of the
+same micro architecture to have slight difference in efficiency due to
+other factors like cache size. Selecting the boost-on-big policy based
+on relative difference in efficiency is not optimal on such systems.
+The boost-policy device tree property is introduced to specify the
+required boost type and it overrides the default selection of boost
+type in the scheduler.
+
+The possible values for this property are "boost-on-big" and "boost-on-all".
+
+Example:
+
+sched-hmp {
+	boost-policy = "boost-on-all"
+}
diff --git a/Documentation/scheduler/sched-hmp.txt b/Documentation/scheduler/sched-hmp.txt
index b400e053e55d..298064bc44d7 100644
--- a/Documentation/scheduler/sched-hmp.txt
+++ b/Documentation/scheduler/sched-hmp.txt
@@ -43,6 +43,7 @@ CONTENTS
    8.8 sched_get_busy
    8.9 sched_freq_alert
    8.10 sched_set_boost
+9. Device Tree bindings
 
 ===============
 1. INTRODUCTION
@@ -1447,3 +1448,10 @@ Logged when boost settings are being changed
 <task>-0     [004] d.h4 12700.711489: sched_set_boost: ref_count=1
 
 - ref_count: A non-zero value indicates boost is in effect
+
+========================
+9. Device Tree bindings
+========================
+
+The device tree bindings for the HMP scheduler are defined in
+Documentation/devicetree/bindings/sched/sched_hmp.txt
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 4b5b0c3cef7a..4cdf967b67c1 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -7812,6 +7812,7 @@ void __init sched_init_smp(void)
 	hotcpu_notifier(cpuset_cpu_inactive, CPU_PRI_CPUSET_INACTIVE);
 
 	update_cluster_topology();
+	init_sched_hmp_boost_policy();
 
 	init_hrtick();
 
@@ -7860,6 +7861,7 @@ void __init sched_init(void)
 
 	BUG_ON(num_possible_cpus() > BITS_PER_LONG);
 
+	sched_hmp_parse_dt();
 	init_clusters();
 
 #ifdef CONFIG_FAIR_GROUP_SCHED
diff --git a/kernel/sched/hmp.c b/kernel/sched/hmp.c
index 61e352aeec00..1e7b4cd4e64c 100644
--- a/kernel/sched/hmp.c
+++ b/kernel/sched/hmp.c
@@ -17,6 +17,7 @@
 #include <linux/cpufreq.h>
 #include <linux/list_sort.h>
 #include <linux/syscore_ops.h>
+#include <linux/of.h>
 
 #include "sched.h"
 #include "core_ctl.h"
@@ -225,6 +226,52 @@ fail:
 	return ret;
 }
 
+/*
+ * It is possible that CPUs of the same micro architecture can have slight
+ * difference in the efficiency due to other factors like cache size. The
+ * BOOST_ON_BIG policy may not be optimial for such systems. The required
+ * boost policy can be specified via device tree to handle this.
+ */
+static int __read_mostly sched_boost_policy = SCHED_BOOST_NONE;
+
+/*
+ * This should be called after clusters are populated and
+ * the respective efficiency values are initialized.
+ */
+void init_sched_hmp_boost_policy(void)
+{
+	/*
+	 * Initialize the boost type here if it is not passed from
+	 * device tree.
+	 */
+	if (sched_boost_policy == SCHED_BOOST_NONE) {
+		if (max_possible_efficiency != min_possible_efficiency)
+			sched_boost_policy = SCHED_BOOST_ON_BIG;
+		else
+			sched_boost_policy = SCHED_BOOST_ON_ALL;
+	}
+}
+
+void sched_hmp_parse_dt(void)
+{
+	struct device_node *sn;
+	const char *boost_policy;
+
+	if (!sched_enable_hmp)
+		return;
+
+	sn = of_find_node_by_path("/sched-hmp");
+	if (!sn)
+		return;
+
+	if (!of_property_read_string(sn, "boost-policy", &boost_policy)) {
+		if (!strcmp(boost_policy, "boost-on-big"))
+			sched_boost_policy = SCHED_BOOST_ON_BIG;
+		else if (!strcmp(boost_policy, "boost-on-all"))
+			sched_boost_policy = SCHED_BOOST_ON_ALL;
+	}
+}
+
 unsigned int max_possible_efficiency = 1;
 unsigned int min_possible_efficiency = UINT_MAX;
 
@@ -1169,12 +1216,9 @@ int task_load_will_fit(struct task_struct *p, u64 task_load, int cpu,
 
 enum sched_boost_type sched_boost_type(void)
 {
-	if (sched_boost()) {
-		if (min_possible_efficiency != max_possible_efficiency)
-			return SCHED_BOOST_ON_BIG;
-		else
-			return SCHED_BOOST_ON_ALL;
-	}
+	if (sched_boost())
+		return sched_boost_policy;
+
 	return SCHED_BOOST_NONE;
 }
 
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 1b641e60233e..ada5e580e968 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1399,6 +1399,8 @@ extern u64 cpu_upmigrate_discourage_read_u64(struct cgroup_subsys_state *css,
 					struct cftype *cft);
 extern int cpu_upmigrate_discourage_write_u64(struct cgroup_subsys_state *css,
 				struct cftype *cft, u64 upmigrate_discourage);
+extern void sched_hmp_parse_dt(void);
+extern void init_sched_hmp_boost_policy(void);
 
 #else	/* CONFIG_SCHED_HMP */
 
@@ -1589,6 +1591,8 @@ static inline void post_big_task_count_change(void) { }
 static inline void set_hmp_defaults(void) { }
 
 static inline void clear_reserved(int cpu) { }
+static inline void sched_hmp_parse_dt(void) {}
+static inline  void init_sched_hmp_boost_policy(void) {}
 
 #define trace_sched_cpu_load(...)
 #define trace_sched_cpu_load_lb(...)