Samsung will present the challenges of creating a dual-Android platform on the Nexus 10 using Xen on ARM. Running two copies of Android is a strong use-case to satisfy the security needs for BYOD (Bring Your Own Device), where one Android can be designated as “work” and is secure and isolated from the users “home” Android. Achieving a good user-experience in both Android is essential for this technology to succeed commercially. The Nexus 10 has ARM Cortex A15 processors. For a good user-experience, both Android need high-performance GPU-accelerated graphics which demand high throughput and low latency. Samsung will discuss the issues encountered using Xen on a mobile device in this demanding use-case, and how the changes for Xen for mobile can be contributed into the community.

1. Dual-AndroidTM on Nexus 10
Samsung Research UK
Presentation
for
Xen Developer Summit
24-25 Oct 2013
Edinburgh, UK
10/21/2013
© Samsung Electronics
1

2. Introduction
 Feasibility: 2 copies of Android on Xen on ARM?
o Xen on mobile performance?
o Virtualized GPU required
 Nexus 10 device used
o
o
o
o
CPU: ARM Cortex A15 (x2)
GPU: ARM Mali T604
Memory available: 2GB RAM, plenty of Flash
Screen resolution: 2560x1504
© Samsung Electronics
2

3. Configuration
 Software configuration – 2 VMs only
o
o
o
o
DOM0 = 1st Android
DOMU = 2nd Android
Linux 3.4
Android Jelly Bean 4.2
 Xen 4.2 for ARM
o Builds on Xen on ARM for Cortex A9 work in Samsung
o Parallel development in Samsung HQ to community
Xen
SMP
I/O
© Samsung Electronics
Dual-core
DOMU kernel
1GB RAM
Memory
DOM0 kernel
1GB RAM
Dual-core
Single-core
Pass through
PV Drivers
3

4. Xen PVH Architecture
DOM0
DOMU
Android
Apps
Android
Apps
Android
Jelly Bean 4.2
Linux 3.4
User
(PL0)
Kernel
(PL1)
Android
Jelly Bean 4.2
Linux 3.4
Physical
Drivers
HYP
(PL2)
HW
Back End
Drivers
Rings
Front End
Drivers
Xen on ARM
Display,
Touch
etc.
© Samsung Electronics
GPU
Mali T604
CPU 0
(Cortex A15)
CPU 1
(Cortex A15)
4

5. Mobile Virtualization
 I/O Challenges – Mobiles have ~50 device drivers
o Sensors: Touch, gyro, proximity, ambient light
o Media: Display, GPU, Camera, Audio, Video
o Connectivity: Charger, USB, WiFi, Bluetooth
 User Switching
o Xen scheduler runs as normal.
o “Foreground” VM – user devices require arbitration driver in DOM0
• Display
• Touch
Display
Switch
Foreground VM
© Samsung Electronics
5

6. Video
 Demo video
o
o
o
o
Switching between Android  Icon or Volume key
Angry Birds in DOMU  Near-native performance of PV drivers
Angry Birds in DOM0 and DOMU concurrently  Two independent Android
3D Benchmark clip
DOM0 – Blue Wallpaper
Passthrough drivers
DOMU – Orange Wallpaper
PV Drivers
Switching icon
© Samsung Electronics
6

7. Near-Native Performance Challenges
 60 frames per second = 16.6ms per frame
o GPU renders each surface  GPU composes the surfaces  frame
 Virtualized graphics options
o API Remoting done above GPU driver for chipset portability
 Android JB has “butter smooth” technology
o Triple buffering
o Needs reliable Vsync interrupt  Xen event channel stressed
o Deferred waiting using sync points & fences
Composition frame buffers
0
1
2
App frame buffers
0
1
2
0
© Samsung Electronics
15
30
45
60
time (ms)
7

8. Results
Dual-Android, GPU composition
70
160
60
140
FPS
100
40
80
30
60
20
Packets/sec (k)
120
50
40
10
20
0
0
DOM0
© Samsung Electronics
DOMU
Packets/sec (k)
8

9. Event Channel Under Stress
 DOMU Vsync arrival time delta
Delta Time (ms)
35
Some
missed
events
30
25
20
16.67
15
10
5
0
10
11
12
13
14
15
16
Benchmark Time (sec)
© Samsung Electronics
17
18
19
20
9

10. Xen For Mobile
 Multi-page ring
o Needed for throughput performance running benchmarks
o Ensure low-latency
 Non-linear grant references
o Old grants are re-used. PV drivers assume linearity
 RAM Allocation limit 512MB
o Buddy allocator is unable to allocate contiguous chunk of memory from the Domheap
memory
 Per-VM interrupts unreliable when stressed
o Must ensure Vsync is received in DOMU with minimal latency
 Contribution to community
o Samsung will work to share Xen changes with community
o Some code is proprietary
© Samsung Electronics
10

11. Conclusion
 Two Android can run with near-native graphics performance
 Xen runs well on mobile devices
 Using PV drivers, no major changes to Xen architecture required
Android is a trademark of Google Inc.
The Android robot is reproduced or modified from work created and shared by Google and used according to terms
described in the Creative Commons 3.0 Attribution License.
Linux® is the registered trademark of Linus Torvalds in the U.S. and other countries.
ARM is a registered trademark of ARM Limited. Mali is a trademark of ARM Limited.
STAR WARS and related properties are trademarks in the United States and/or in other countries of Lucasfilm Ltd. and/or
its affiliates. © 2012 Lucasfilm Ltd. All rights reserved.
Angry Birds is a trademark of Rovio Entertainment Ltd.
© Samsung Electronics
11