Cells: A Virtual Mobile Smartphone Architecture(2011) Fumitoshi Mizutani and Yerzhan Yerbolat Mobile and Cloud Computing

MOTIVATION AND PROBLEM DEFINITION Disable software installation No camera on secret places Employees Test prototype software Application developers Can let their children to play with phone(safely) Parents Extra phone

How to put two systems on one device? Hypervisor(traditional solution) Type2 (Host) Type1(Bare metal) Hardware Host OS Regular Process emulator Gest OS Hardware Hypervisor Gest OS Regular Process .

Hypervisor Type1 Advantage: Disadvantage Hardware Hypervisor Gest OS Regular Process 1960s IBM developed CP/CMS Usually for big servers Advantage: Linux has standard Hypervisor function from 2.6.20 called Kernel based Virtual Machine (KVM); Some CPU support virtualization acceleration ,Intel VT-x, AMD-V. Disadvantage Requires huge Hardware power.

Hypervisor Type2 Well known emulators are: VM Player; Game HW emulators – Nintendo. Benefits: Easy to install; Portable; Image can copy to different machine and resume Can run different Gest OS Drawbacks: Require rich Hardware resource OS overhead is large Hardware Host OS Regular Process emulator Gest OS

OS Virtualization New Introduced in 2002 by Steven Osman Hardware OS OS Virtualize layer Virtual environment Introduced in 2002 by Steven Osman “The Design and Implementation of Zap” Benefits: Easy to maximize performance of Software and Hardware; Easy to manage Software and Hardware; Can provide high efficiency. Drawbacks: Need to think carefully about isolation of each Virtual OS; Many devices on Smart phone are not designed to be shared concurrently. Difficult to move to new machine

RELATED WORK Cells was first in its kind that use OS virtualization on smart phone: Xen for ARM , J. Hwang, 2008 (Hypervisor Type1) Xen project, started at University of Cambridge; Open source . KVM/ARM, C. Dall, 2010 (Hypervisor Type1) Written by same authors as cells; Needed to optimize kernel to optimize performance. VMware Mobile Virtualization Platform,K.Barr,2010 ( Hypervisor Type2) Android OS. Commercial product

Cells (OS Virtualization layer) MAIN CONTRIBUTIONS Cells showed the way to virtualize Smartphone by using OS virtualization; Cells created multi-phone environment with nearly zero runtime overhead. Hardware Android OS Cells (OS Virtualization layer) Virtual Phone Virtual Phone

Cells design Foreground and background Virtual Phone(VP): allow one single VP to be displayed on screen (foreground VP); The other VP can receive event and perform task (background VP) For example: can receive a call!!! Each VP can be set not to use specific device: For example : No access to camera, make a call, network.

How do devices manage the choice of foreground or background VP ? Virtual Phone 1 Virtual Phone 2 Virtual Phone 3 GPU Device Namespace Wrapper GPS Input Linux Kernel ID_GPUVP1 ID_GPUVP2 ID_GPUVP3 GPS_VP1 GPS_VP2 GPS_VP3 Input_VP1 Input_VP2 Input_VP3 F

How does VPs hold device configuration? Linux Kernel Virtual Phone Root Space Cell D Device Config Inter Process Communication(IPC) User space

How Cells do isolation of VP? Use UID in Linux System to set user credential User from one VP can not install applications on another VP; Use Device Namespace isolation VP can not have access outside of VP’s device namespace Use different mount space for each VP VP cannot access others VP’s files

TELEPHONY Android Java Android Java Java Phone/Radio Interface Layer(RIL) Java Phone/Radio Interface Layer(RIL) RIL Daemon RIL Daemon Cell D Black box Cells RIL Vendor RIL Vendor RIL Black box Kernel Kernel Drivers/PPP Drivers/PPP Base band Base band GSM/CDMA GSM/CDMA

EXPERIMENTAL RESULTS Experiment aim to measure: runtime overhead; power consumption; memory usage. Testing configuration: Up to 5 Virtual phones; With App and NoApp modes; Network test downloading 400 Mb file using wi-fi; Power consumption test 4 and 12 hours Active and Idle modes.

Equipment Software: Hardware: Android 2.1 Eclair, Android 2.3 Gingerbread; As a workload daily applications: Browser, Mail client, Calendar. 5 benchmark applications to measure CPU, GPU, File I/O, Network and Web browsing. Hardware: Samsung nb30 laptop(1.66 GHz Intel Atom, 1 Gb RAM) as a Server for network test. Nexus 1 smartphone Qualcomm 1GHz Adreno 200 GPU 512 Mb RAM, 1400 mAh Patriot class 10 SD Card. Nexus S smartphone Hummingbird 1GHz 200 MHz PowerVR GPU 512 Mb RAM 1500 mAh Internal Flash memory

Runtime overhead(Baseline) Figure 8: No App mode, Nexus 1 perform worse than Nexus S on Quadrant(File I/O) and Network tests(might be SD card usage). Overall performance overhead of Cells was within 7% in comparison to Baseline(original). Jeremy Andrus et al. , Cells: A Virtual Mobile Smartphone Architecture, p184 Figure 3, 2011

Runtime overhead(With App) Figure 9: In “With App” mode background music was continuously played during the test. Performance of Nexus S shown less than 10% overhead. Jeremy Andrus et al. , Cells: A Virtual Mobile Smartphone Architecture, p184 Figure 3, 2011

Power consumption Figure 10: Power consumption in active mode 4 hours and 12 passive mode. Nexus 1 during playing the music shows gradual increase up to 20% overhead because of scheduling more processes. While on Nexus S power overhead was within 2%. Jeremy Andrus et al. , Cells: A Virtual Mobile Smartphone Architecture, p184 Figure 3, 2011

Memory usage Figure 11: Memory test in “Apps mode” running applications such as Web browser, mail client, Calendar on all VPs. Nexus 1 show 20% better result because of Kernel Same page Merging algorithm(KSM). Nexus S use Low memory killer that free the memory during the execution 4th VP in “No Apps” mode and after 3rd VP in “Apps” mode. Jeremy Andrus et al. , Cells: A Virtual Mobile Smartphone Architecture, p184 Figure 3, 2011

FUTURE WORK The areas that might be developed in future: Cross-platform Cells Virtualization that can run on different OS-s: IOS, Windows Mobile, RIM; Test the security and isolation of VP; Display several VP Desktops on one screen; How to upgrade hardware?

CONCLUSION OS virtualization on smartphones is a complex issue. It has constraints in terms of wide range of devices in each smartphone, sharing each of them concurrently and isolating VPs from each other. Cell virtualization has shown that OS virtualization is possible on smartphones and has good performance. Experiments has shown that runtime overhead was nearly zero and might be more visible if they do more testing. However, some questions left unanswered: “How reliable the security of the VPs? How to upgrade hardware or move to new smart phone?”