Xen.org community presentation from Xen Summit Asia 2

1. Graphics Pass-through with VT-d
Nov-19-2009
Weidong Han
Ben Lin
Xen Summit Asia 2009

2. Agenda
• Graphics Virtualization Introduction
• Graphics Pass-through with VT-d
• Performance
• Conclusion
Software and Services Group
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3. Requirements on Graphics Virtualization
• Require graphics capabilities Virtual Machine
in virtualization environment
3D
— 3D games Game
— High definition video playback
HD
— CAD Video
CAD
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4. Approaches
• Device emulation
Emulate a graphics device
— Sharing amongst guests
— High overhead in emulation
• Graphics API remoting
Forward graphics API calls from guest to the external graphics stack via remote
procedure call
— Hardware independent
— Need additional software stacks in guest
• Pass-through
Direct access graphics device in guest
— Good performance
— Don’t require any special knowledge of GPU programming interfaces
— Dedicate the graphics device to one guest
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5. Agenda
• Graphics Virtualization Introduction
• Graphics Pass-through with VT-d
• Performance
• Conclusion
Software and Services Group
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6. PCI Pass-through with VT-d
• Assign a physical device to a guest
directly
Domain 0 Domain 1
• Guest accesses the device directly Native
with minimal hypervisor intervention driver
QEMU
• Physical device accesses guest’s
memory directly with help of VT-d
Xen Hypervisor
• Interrupt will be injected to guest
through hypervisor
Hardware
• PCI Configuration Space Access
needs trap-and-emulation
Software and Services Group
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7. Challenges of Graphics Pass-through
• Legacy VGA resources
— Legacy VGA I/O ports and frame buffers are at fixed locations
• I/O ports: 0x3B0 – 0x3BB, 0x3C0 – 0x3DF
• Frame buffer: 0xA0000 – 0xBFFFF
• Graphics device re-initialization in guest
— Execute Video BIOS
— But Video BIOS bits may be truncated or modified after initialization in host, thus
cannot be re-executed correctly
• Secondary graphics pass-through
— The secondary graphics device doesn’t claim VGA cycle
• Additional challenges on integrated graphics device (IGD)
— May have assumptions on host chipset or BIOS
Software and Services Group
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8. Primary Discrete Graphics Device
• Legacy VGA resources
— 1:1 map legacy VGA resources
• Video BIOS
For Video BIOS without re-execution issue:
— Extract video BIOS from host address 0xC0000
— Copy video BIOS to guest address 0xC0000
For Video BIOS with re-execution issue:
— Get video BIOS from graphics device via tools (e.g. NiBiTor)
— Load video BIOS file to guest ROMs
— Copy video BIOS to guest address 0xC0000
Software and Services Group
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9. Secondary Discrete Graphics Device
• Legacy VGA resources
— 1:1 map legacy VGA resources
• Video BIOS
— Get video BIOS from graphics device via tools (e.g. NiBiTor)
— Load video BIOS file to guest ROMs
— Copy video BIOS to guest address 0xC0000
• Claim VGA cycle
— Enable VGA on its PCI bridge
Software and Services Group
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10. Intel Integrated Graphics Device
• Extra changes required to handle assumptions on host chipset or BIOS
• Intel Q45 IGD:
— Assumptions on chipset
• Graphics Control Register: 0x52 – 0x53
– Specify the amount of graphics memory allocated from system memory
• Vendor ID and Device ID
– Linux loads its driver only if it’s a compatible chipset
Solution: Pass-through some registers of host bridge
— Assumptions on device BDF (Bus:Device.Function)
• Video BIOS hardcode the BDF to 00:02.0
Solution: Assign BDF 00:02.0 to IGD in guest
— Vendor specific FLR (Function Level Reset)
• FLR capability is not exposed,
Solution: need specific logic to locate it and perform FLR
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11. Agenda
• Graphics Virtualization Introduction
• Graphics Pass-through with VT-d
• Performance
• Conclusion
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12. Test Environment
• GPU: Intel Integrated Graphics on Intel Q45 Chipset
• Native
— One CPU
— Memory 1G
• Guest
— One Virtual CPU
— Memory 1G
• Operating System
— Vista Enterprise 32-bit
— WDDM driver
• Xen 3.4
• 3DMark06
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13. 1.3148E-10
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Results
Return To Proxycon
Firefly Forest
CPU1 - Red Valley
CPU2 - Red Valley
Fill Rate - Single-Texturing
Fill Rate - Multi-Texturing
Pixel Shader
Vertex Shader - Simple
Vertex Shader - Complex
HDR-1
HDR-2
Software and Services Group
Perlin noise
Guest/Native
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14. Agenda
• Graphics Virtualization Introduction
• Graphics Pass-through with VT-d
• Performance
• Conclusion
Software and Services Group
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15. Conclusion
• Graphics pass-through has special challenges
• Xen now supports graphics pass-through:
— IGD pass-through patch was sent out in xen-devel mailing list, still under
review
• Graphics pass-through achieves good performance
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16. Questions?
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17. Backup
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18. Specific Hacks for Graphics Pass-through
• Some graphics devices are virtualization unfriendly
• 1:1 map physical BARs and virtual BARs
— Some discrete graphics devices (e.g. nVidia Geforce 8400 GS) seem to
use the BAR registers in hardware for address decoding of memory
requests
• Don’t remove shadows of MMIO direct
— When pass-through some graphics devices to Vista or Win7 guest, it will
remove shadows of MMIO direct, then results in system crash
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19. Legal Information
INFORMATION IN THIS DOCUMENT IS PROVIDED IN CONNECTION WITH INTEL PRODUCTS.
NO LICENSE, EXPRESS OR IMPLIED, BY ESTOPPEL OR OTHERWISE, TO ANY INTELLECTUAL
PROPERTY RIGHTS IS GRANTED BY THIS DOCUMENT. EXCEPT AS PROVIDED IN INTEL'S
TERMS AND CONDITIONS OF SALE FOR SUCH PRODUCTS, INTEL ASSUMES NO LIABILITY
WHATSOEVER AND INTEL DISCLAIMS ANY EXPRESS OR IMPLIED WARRANTY, RELATING
TO SALE AND/OR USE OF INTEL PRODUCTS INCLUDING LIABILITY OR WARRANTIES
RELATING TO FITNESS FOR A PARTICULAR PURPOSE, MERCHANTABILITY, OR
INFRINGEMENT OF ANY PATENT, COPYRIGHT OR OTHER INTELLECTUAL PROPERTY RIGHT.
Intel may make changes to specifications, product descriptions, and plans at any time,
without notice.
All products, computer systems, dates, and figures specified are preliminary based on
current expectations, and are subject to change without notice.
Performance tests and ratings are measured using specific computer systems and/or
components and reflect the approximate performance of Intel products as measured by
those tests. Any difference in system hardware or software design or configuration may
affect actual performance.
Intel is a trademark of Intel Corporation in the U.S. and other countries.
*Other names and brands may be claimed as the property of others.
Copyright © 2009, Intel Corporation. All rights are protected.
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20. Software and Services Group
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