ANDROID: sched/tune: add initial support for CGroups based boosting

To support task performance boosting, the usage of a single knob has the
advantage to be a simple solution, both from the implementation and the
usability standpoint.  However, on a real system it can be difficult to
identify a single value for the knob which fits the needs of multiple
different tasks. For example, some kernel threads and/or user-space
background services should be better managed the "standard" way while we
still want to be able to boost the performance of specific workloads.

In order to improve the flexibility of the task boosting mechanism this
patch is the first of a small series which extends the previous
implementation to introduce a "per task group" support.
This first patch introduces just the basic CGroups support, a new
"schedtune" CGroups controller is added which allows to configure
different boost value for different groups of tasks.
To keep the implementation simple but still effective for a boosting
strategy, the new controller:
  1. allows only a two layer hierarchy
  2. supports only a limited number of boost groups

A two layer hierarchy allows to place each task either:
  a) in the root control group
     thus being subject to a system-wide boosting value
  b) in a child of the root group
     thus being subject to the specific boost value defined by that
     "boost group"

The limited number of "boost groups" supported is mainly motivated by
the observation that in a real system it could be useful to have only
few classes of tasks which deserve different treatment.
For example, background vs foreground or interactive vs low-priority.
As an additional benefit, a limited number of boost groups allows also
to have a simpler implementation especially for the code required to
compute the boost value for CPUs which have runnable tasks belonging to
different boost groups.

cc: Tejun Heo <tj@kernel.org>
cc: Li Zefan <lizefan@huawei.com>
cc: Johannes Weiner <hannes@cmpxchg.org>
cc: Ingo Molnar <mingo@redhat.com>
cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Patrick Bellasi <patrick.bellasi@arm.com>
Signed-off-by: Andres Oportus <andresoportus@google.com>

init/Kconfig

@@ -971,6 +971,82 @@ menuconfig CGROUPS
 
 if CGROUPS
 
+config CGROUP_DEBUG
+	bool "Example debug cgroup subsystem"
+	default n
+	help
+	  This option enables a simple cgroup subsystem that
+	  exports useful debugging information about the cgroups
+	  framework.
+
+	  Say N if unsure.
+
+config CGROUP_FREEZER
+	bool "Freezer cgroup subsystem"
+	help
+	  Provides a way to freeze and unfreeze all tasks in a
+	  cgroup.
+
+config CGROUP_PIDS
+	bool "PIDs cgroup subsystem"
+	help
+	  Provides enforcement of process number limits in the scope of a
+	  cgroup. Any attempt to fork more processes than is allowed in the
+	  cgroup will fail. PIDs are fundamentally a global resource because it
+	  is fairly trivial to reach PID exhaustion before you reach even a
+	  conservative kmemcg limit. As a result, it is possible to grind a
+	  system to halt without being limited by other cgroup policies. The
+	  PIDs cgroup subsystem is designed to stop this from happening.
+
+	  It should be noted that organisational operations (such as attaching
+	  to a cgroup hierarchy will *not* be blocked by the PIDs subsystem),
+	  since the PIDs limit only affects a process's ability to fork, not to
+	  attach to a cgroup.
+
+config CGROUP_DEVICE
+	bool "Device controller for cgroups"
+	help
+	  Provides a cgroup implementing whitelists for devices which
+	  a process in the cgroup can mknod or open.
+
+config CPUSETS
+	bool "Cpuset support"
+	help
+	  This option will let you create and manage CPUSETs which
+	  allow dynamically partitioning a system into sets of CPUs and
+	  Memory Nodes and assigning tasks to run only within those sets.
+	  This is primarily useful on large SMP or NUMA systems.
+
+	  Say N if unsure.
+
+config PROC_PID_CPUSET
+	bool "Include legacy /proc/<pid>/cpuset file"
+	depends on CPUSETS
+	default y
+
+config CGROUP_CPUACCT
+	bool "Simple CPU accounting cgroup subsystem"
+	help
+	  Provides a simple Resource Controller for monitoring the
+	  total CPU consumed by the tasks in a cgroup.
+
+config CGROUP_SCHEDTUNE
+	bool "CFS tasks boosting cgroup subsystem (EXPERIMENTAL)"
+	depends on SCHED_TUNE
+	help
+	  This option provides the "schedtune" controller which improves the
+	  flexibility of the task boosting mechanism by introducing the support
+	  to define "per task" boost values.
+
+	  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
+
+	  Say N if unsure.
+
 config PAGE_COUNTER
        bool