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

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".

Change-Id: Iac19183fa7d4bfd9e5746b02a02b2b19cf64b78d
Signed-off-by: Pavankumar Kondeti <pkondeti@codeaurora.org>

2 files changed, 43 insertions, 0 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