background introduction android os architecture feasibility and necessity android rts architecture...
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Background Introduction
Android OS Architecture
Feasibility and Necessity
Android RTS ArchitectureLimitation
Improvement
Lei Cui
Evaluating Android OS for Embedded Real-
Time System
Background IntroductionAndroid platform has been instantly improved either in terms of features or supported hardware, as well as the extension-based new types of devices, which has attracted much attention from the various industries fields gradually. In other words, the utilization of Android OS based on Linux kernel has covered the whole daily life related to the E-control.
However, there is a feature that has not been explored yet - the RT capabilities. This paper provides an idea of adding some RT features into Android platform to make it a RT architecture in order to be used in open real-time environment.
Android OS Architecture
Android Architecture
Application Uppermost layer; a core set of applications; out of the box
ApplicationFramework
APIs; Services;
Libraries libc: the standard C system library for embedded Linux-based devices
Android Runtime
Android VM (Dalvik): target for memory/CPU-constrained devices; Infinite register-based machine
Linux Kernel
Drivers; Resource Management; Power Management; Hardware Control Management, etc; HAL: interaction with HW via Drivers
Details of Android Architecture
Android OS Architecture(DVM)1. Why does Android architecture utilize DVM but JVM?
Less instruction dispatch and memory access——30%Less CPU resource and computation timeMore bytes in the instruction stream——35%
2. What is the principle of Dalvik VM?
Dalvik-VM
Linux Kernel
Resource Management Capability
Feasibility and Necessity
Feasibility and Necessity(Dalvik-VM)
Fork()
VM father process
Child processes
Pre-initialization&
Pre-loadingOf Android APIs and Classes
(initial Andriod Runtime & setup VM)
All the scheduling
activities are delegated by the VM to the
kernel
Feasibility and Necessity(Linux Kernel)
Feasibility and Necessity(Resource Management Capability)
Android RTS Architecture
Android Full RT Platform
Prospredict priority inversion; better resource management; more-seamless integration; predictability and determinism;ConsDrivers supported natively implement during integration phase; Android Extended
Difference(RTSJ)
Both works ensure resource reservation & RT tasks scheduling in order to guarantee resource bandwidth to apps, within an interval of time
Pros: beneficial for incorporating a more deterministic RT behavior in the VM level;
Con: keep up with release cycle of Android
Pros: bound-based memory management; RT scheduler in RT-JVM; better synchronisation mechanisms; avoid priority inversion;Cons: integration issues
Android RTS Architecture
Android Partly RT Android with a RT Hypervisor
Guest OS
Parallel
High PriorityHigh Priority
No need for VM
Apps that need VM will not benefit from this model
Apps are limited by RT Hypervisor;If RT apps hangs, the sys may hang;
Low Integration
RT Linux Limitation
1. Linux system scheduling unit is 10ms, which is coarse-granularity and cannot provide the precise timing;
2. Until now, when a task or process is called into kernel state from userland it is unpreempted that cannot guarantee the predictability & undeterministics;
3. The utilization of virtual memory technology;
4. …….
5. Lack of effective and efficient RT scheduling algorithms & policies;
Improvement
1. Improve the accuracy of the CPU clock via Clock Counter Register to solve the Linux coarse-granularity issues; eg. RT-Linux & Kurt-Linux;
2. By insert preempted points into kernel functions to solve unpreempted issues that cannot guarantee the predictability & undeterministics; for instance, RED-Linux;
3. …….
4. Define OS scheduling RT framework & algorithms to solve the issues lack of effective and efficient RT scheduling algorithms & policies; RED-Linux, Qlinux, H-SFQ, Cello, SILK, etc.
Background Introduction
Architecture
Implementation & Evaluation
Lei Cui
Real-Time Android: Deterministic Ease of Use
Background IntroductionThe preferences of end-usersDevelopers with consistent usability A convenient development environment
Android Platform(upper)
Rich & Mature feature set Linux Kernel(bottom)
Android Architecture
Android stack with RT capabilitiesin a minimally invasive way via adding a crucial Linux building block
Exclusive concern in the industrial embedded domain
Remedies for user & programmerof embedded RTS
Architecture
Linux Kernel(Kernel State)
Android Framework (User State)
Communication & Data exchange
Architecture---Linux Kernel
RT support by the OS kernel is obviously a mandatory requirement for RT architectures
RTAIRTLinux,Xenomai
Preempt_rtLitmus-RT
…Preempt_rt is not a RT kernel owing to the complexity of the Linux kernel
——impossible to prove upper bounds on all operations under all possible circumstances——allow to determine upper latency bounds
Architecture--- User State
Android Full RT Platform Android Extended
The Android userland is heavily based on the Dalvik VM, based on register rather than stack architecture. Obsolete--why
Exceed constrained developer resources
Provide an insufficient return on investment
Linux C without translation by VM
Architecture--- Data exchange
Communication Channel
Reject unbounded delays
Shared-memory & Mutual exclusion avoid data corruptionEasily result in unbounded
latenciesShared-memory & Synchronization algorithm lock-free & wait-free
Implementation & Evaluation
A. Basis Component IntegrationBased on the preempt_rt release 2.6.33, back-
port the BSP from 36 to 33, and forward-port the Android patch set from 32 to 33.
B. Shared-memory
1. A system service creates a shared-memory via mmap() sys call;2. The service registers at Binder;3. All programs acquire reference via Binder call; 4. Native clients receive pointer directly;JNI library provides access methods to Android apps.
Implementation & EvaluationC. Demo
D. Latency Measurements E. Efforts
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