ANDROID: sched: Introduce Window Assisted Load Tracking (WALT)

use a window based view of time in order to track task
demand and CPU utilization in the scheduler.

Window Assisted Load Tracking (WALT) implementation credits:
 Srivatsa Vaddagiri, Steve Muckle, Syed Rameez Mustafa, Joonwoo Park,
 Pavan Kumar Kondeti, Olav Haugan

2016-03-06: Integration with EAS/refactoring by Vikram Mulukutla
            and Todd Kjos

Change-Id: I21408236836625d4e7d7de1843d20ed5ff36c708

Includes fixes for issues:

eas/walt: Use walt_ktime_clock() instead of ktime_get_ns() to avoid a
race resulting in watchdog resets
BUG: 29353986
Change-Id: Ic1820e22a136f7c7ebd6f42e15f14d470f6bbbdb

Handle walt accounting anomoly during resume

During resume, there is a corner case where on wakeup, a task's
prev_runnable_sum can go negative. This is a workaround that
fixes the condition and warns (instead of crashing).

BUG: 29464099
Change-Id: I173e7874324b31a3584435530281708145773508

Signed-off-by: Todd Kjos <tkjos@google.com>
Signed-off-by: Srinath Sridharan <srinathsr@google.com>
Signed-off-by: Juri Lelli <juri.lelli@arm.com>
[jstultz: fwdported to 4.4]
Signed-off-by: John Stultz <john.stultz@linaro.org>
Signed-off-by: Andres Oportus <andresoportus@google.com>

init/Kconfig

@@ -400,6 +400,15 @@ config IRQ_TIME_ACCOUNTING
 
 	  If in doubt, say N here.
 
+config SCHED_WALT
+        bool "Support window based load tracking"
+        depends on SMP
+        help
+        This feature will allow the scheduler to maintain a tunable window
+	based set of metrics for tasks and runqueues. These metrics can be
+	used to guide task placement as well as task frequency requirements
+	for cpufreq governors.
+
 config BSD_PROCESS_ACCT
 	bool "BSD Process Accounting"
 	depends on MULTIUSER