Merge "Update TARE README." into tm-dev

apex/jobscheduler/service/java/com/android/server/tare/README.md

@@ -1,10 +1,12 @@
+# Overview
+
 Welcome to The Android Resource Economy (TARE for short). If you're reading this, you may be
 wondering what all of this code is for and what it means. TARE is an attempt to apply economic
 principles to resource (principally battery) management. It acknowledges that battery is a limited
 resource on mobile devices and that the system must allocate and apportion those resources
-accordingly. Every action (running a job, firing an alarm, using the network, using the CPU,
-etc.) has a cost. Once that action has been performed and that bit of battery has been drained, it's
-no longer available for someone else (another app) to use until the user charges the device again.
+accordingly. Every action (running a job, firing an alarm, using the network, using the CPU, etc.)
+has a cost. Once that action has been performed and that bit of battery has been drained, it's no
+longer available for someone else (another app) to use until the user charges the device again.
 
 The key tenets of TARE are:
 
@@ -13,10 +15,22 @@ The key tenets of TARE are:
 1. Reward for good actions --- reward and encourage behavior that provides value to the user
 1. Fine bad actions --- fine and discourage behavior that is bad for the user
 
-# Details
+In an ideal world, the system could be said to most efficiently allocate resources by maximizing its
+profits — by maximizing the aggregate sum of the difference between an action's price (that
+the app ends up paying) and the cost to produce by the system. This assumes that more important
+actions have a higher price than less important actions. With this assumption, maximizing profits
+implies that the system runs the most important work first and proceeds in decreasing order of
+importance. Of course, that also means the system will not run anything where an app would pay less
+for the action than the system's cost to produce that action. Some of this breaks down when we throw
+TOP apps into the mix — TOP apps pay 0 for all actions, even though the CTP may be greater
+than 0. This is to ensure ideal user experience for the app the user is actively interacting with.
+Similar caveats exist for system-critical processes (such as the OS itself) and apps running
+foreground services (since those could be critical to user experience, as is the case for media and
+navigation apps). Excluding those caveats/special situations, maximizing profits of actions
+performed by apps in the background should be the target.
 
-To achieve the goal laid out by TARE, we introduce the concept of Android Resource Credits
-(ARCs for short).
+To achieve the goal laid out by TARE, we use Android Resource Credits (ARCs for short) as the
+internal/representative currency of the system.
 
 ## How do ARCs work?
 
@@ -36,6 +50,57 @@ all of its ARCs for jobs if it doesn't want to schedule any alarms.
 With the ARC system, we can limit the total number of ARCs in circulation, thus limiting how much
 total work can be done, regardless of how many apps the user has installed.
 
+## EconomicPolicy
+
+An EconomicPolicy defines the actions and rewards a specific subsystem makes use of. Each subsystem
+will likely have a unique set of actions that apps can perform, and may choose to reward apps for
+certain behaviors. Generally, the app should be rewarded with ARCs for behaviors that indicate that
+the app provided value to the user. The current set of behaviors that apps may be rewarded for
+include 1) a user seeing a notification, 2) a user interacting with a notification, 3) the user
+opening the app and/or staying in the app for some period of time, 4) the user interacting with a
+widget, and 5) the user explicitly interacting with the app in some other way. These behaviors may
+change as we determine better ways of identifying providing value to the user and/or user desire for
+the app to perform the actions it's requesting.
+
+### Consumption Limit
+
+The consumption limit represents the maximum amount of resources available to be consumed. When the
+battery is satiated (at 100%), then the amount of resources available to be consumed is equal to the
+consumption limit. Each action has a cost to produce that action. When the action is performed,
+those resources are consumed. Thus, when an action is performed, the action's CTP is deducted from
+the remaining amount of resources available. In keeping with the tenet that resources are limited
+and ARCs are a proxy for battery consumption, the amount of resources available to be consumed are
+adjusted as the battery level changes. That is, the consumption limit is scaled based on the current
+battery level, and if the amount currently available to be consumed is greater than the scaled
+consumption limit, then the available resources are decreased to match the scaled limit.
+
+### Regulation
+
+Regulations are unique events invoked by the ~~government~~ system in order to get the whole economy
+moving smoothly.
+
+# Previous Implementations
+
+## V0
+
+The initial implementation/proposal combined the supply of resources with the allocation in a single
+mechanism. It defined the maximum number of resources (ARCs) available at a time, and then divided
+(allocated) that number among the installed apps, intending to have some left over that could be
+allocated as part of the rewards. There were several problems with that mechanism:
+
+1. Not all apps used their credits, which meant that allocating credits to those packages
+   effectively permanently reduced the number of usable/re-allocatable ARCs.
+1. Having a global maximum circulation spread across multiple apps meant that as more apps were
+   installed, the allocation to each app decreased. Eventually (with enough apps installed), no app
+   would be given enough credits to perform any actions.
+
+These problems effectively meant that misallocation was a big problem, demand wasn't well reflected,
+and some apps may not have been able to perform work even though they otherwise should have been.
+
+Tare Improvement Proposal #1 (TIP1) separated allocation (to apps) from supply (by the system) and
+allowed apps to accrue credits as appropriate while still limiting the total number of credits
+consumed.
+
 # Definitions
 
 * ARC: Android Resource Credits are the "currency" units used as an abstraction layer over the real