ANDROID: sched: fair/tune: Add schedtune with cgroups interface

Schedtune is the framework we use in Android to allow userspace
task classification and provides a CGroup controller which has two
attributes per group.

 * schedtune.boost
 * schedtune.prefer_idle

Schedtune itself provides task and CPU utilization boosting. EAS in
the fair scheduler uses boosted utilization and prefer_idle status to
control the algorithm used for wakeup task placement.

Boosting:

The task utilization signal, which is derived from PELT signals and
properly scaled to be architecture and frequency invariant, is used by
EAS as an estimation of the task requirements in terms of CPU bandwidth.

Schedtune allows userspace to assign a percentage boost to each group
and this boost is used to calculate an additional utilization margin.
The margin added to the original utilization is:
 1. computed based on the "boosting strategy" in use
 2. proportional to boost value defined by the "taskgroup" value

The boosted signal is used by EAS for task placement, and boosted CPU
utilization (if boosted tasks are running) is given when schedutil
requests utilization.

Prefer_idle:

When this attribute is 1 for a group, this is used as a signal from
userspace that tasks in this group need to be serviced with the
minimum latency possible.

Previous versions of schedtune had much more functionality around
allowing a more tuneable tradeoff between performand and energy,
however this has not been used a lot up until now. If necessary,
we can easily resurrect it based upon old code.

Change-Id: Ie2fd63d82f604f34bcbc7e1ca9b5af1bdcc037e0
Signed-off-by: Patrick Bellasi <patrick.bellasi@arm.com>
Signed-off-by: Chris Redpath <chris.redpath@arm.com>

1 files changed, 23 insertions, 0 deletions

diff --git a/init/Kconfig b/init/Kconfig
index 0e4f10d48d86..de490d85a2ee 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -959,6 +959,29 @@ config SCHED_AUTOGROUP
 	  desktop applications.  Task group autogeneration is currently based
 	  upon task session.
 
+config SCHED_TUNE
+	bool "Boosting for CFS tasks (EXPERIMENTAL)"
+	depends on SMP
+	help
+	  This option enables support for task classification using a new
+	  cgroup controller, schedtune. Schedtune allows tasks to be given
+	  a boost value and marked as latency-sensitive or not. This option
+	  provides the "schedtune" controller.
+
+	  This new controller:
+	  1. allows only a two layers hierarchy, where the root defines the
+	     system-wide boost value and its direct childrens define each one a
+	     different "class of tasks" to be boosted with a different value
+	  2. supports up to 16 different task classes, each one which could be
+	     configured with a different boost value
+
+	  Latency-sensitive tasks are not subject to energy-aware wakeup
+	  task placement. The boost value assigned to tasks is used to
+	  influence task placement and CPU frequency selection (if
+	  utilization-driven frequency selection is in use).
+
+	  If unsure, say N.
+
 config DEFAULT_USE_ENERGY_AWARE
 	bool "Default to enabling the Energy Aware Scheduler feature"
 	default n