Srinivas Kalaga from Samsung Research UK talks about running 2 instances of the Android OS on the same hardware (Nexus 10) via Xen.

1. Dual-AndroidTM on Nexus 10
Samsung Research UK
Presentation
for
FOSDEM 2014
2/11/2014
© Samsung Electronics
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2. Introduction
 Feasibility: 2 copies of Android on Xen on ARM?
o Xen on mobile performance?
o Virtualized GPU required
 Nexus 10 device used (SoC: Samsung Exynos 5250)
o
o
o
o
CPU: ARM Cortex A15 (x2) : With virtualization extensions
GPU: ARM Mali T604 (OpenGl ES2.0)
Memory available: 2GB RAM, plenty of Flash
Screen resolution: 2560x1504
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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 Virtualization extensions support
•
•
•
•
•
vGIC2
Two stage translation page tables, guest memory isolation by hardware.
Generic timer for Hypervisor timer
Neon SIMD support
IOMMU (not fully supported yet so IPA=PA)
 Parallel development in Samsung HQ to community
Xen
SMP
I/O
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Dual-core
DOMU kernel
1GB RAM
Memory
DOM0 kernel
1GB RAM
Dual-core
Single-core
Pass through
PV Drivers
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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.
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GPU
Mali T604
CPU 0
(Cortex A15)
CPU 1
(Cortex A15)
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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
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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
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7. Android UI virtualization challenges
 Android Jelly Bean
o
o
o
o
o
Project Butter: Buttery smooth UI
Triple buffering using ION memory allocated buffers, no FBdev
New sync mechanism via fences.
Hardware composition for the Surfaces
So rendering to display is all closely integrated within the OS frameworks and
Kernel Subsystems (Surfaceflinger, Surfaceview, Gralloc , ION memory
allocator, Fence-sync, Display driver).
 Para-virtualization of ION, Fence-Sync and Display using grant-memory and
eventchannels.
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8. 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
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15
30
45
60
time (ms)
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9. 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
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DOMU
Packets/sec (k)
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10. 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)
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18
19
20
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11. 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
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12. 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.
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13. Q&A
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