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

2. 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

3. 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 .

4. 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 called Kernel based Virtual Machine (KVM);
Some CPU support virtualization acceleration ,Intel VT-x, AMD-V.
Disadvantage
Requires huge Hardware power.

5. 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

6. 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

7. 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

8. 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

9. 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.

10. 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

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

12. 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

13. 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

14. 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.

15. 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

16. 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

17. 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

18. 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

19. 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

20. 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?

21. 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?”