Xen Project 4.4: Features and Futures

Russell Pavlicek
Xen Project Evangelist, Citrix
Systems

Xen Project 4.4 Features

Improved Flexibility in Driver Domains
• Linux driver domains used to rely on udev events in
order to launch backends for guests
– Dependency on udev is replaced with a custom daemon
built on top of libxl
– Provides greater flexibility in order to run user-space
backends inside of driver domains
– Example of capability: driver domains can now use
Qdisk backends, which was not possible with udev

Improved Event Channel Scalability
• Event channels are para-virtualized interrupts
• Previously limited to either 1024 or 4096 channels
per domain
– Domain 0 needs several event channels for each guest
VM (for network/disk backends, qemu etc.)
– Practical limit of total number of VMs to around 300500 (depending on VM configuration)

Improved Event Channel Scalability (2)
• New FIFO-based event channel ABI allows for over
100,000 event channels
– Improve fairness
– Allows for multiple priorities
– The increased limit allows for more VMs, which benefits
large systems and cloud operating systems such as
MirageOS, ErlangOnXen, OSv, HalVM

Experimental PVH Support
• PVH mode combines the best elements of HVM and
PV
– PVH takes advantage of many of the hardware
virtualization features that exist in contemporary
hardware

• Potential for significantly increased efficiency and
performance
• Reduced footprint in Linux and FreeBSD

Tech Preview of Nested Virtualization
• Nested virtualization provides virtualized hardware
virtualization extensions to guests
– Can now run Xen Project, KVM, VMWare or HyperV
inside of a guest for debugging or deployment testing
– Also allows Windows 7 "XP Compatibility mode"
– Tech Preview not yet ready for production use, but has
made significant gains in functionality and reliability

• More information on nested virtualization: see Xen
nested

Improved Support for SPICE
• SPICE is a protocol for virtual desktops which allows
a much richer connection than display-only
protocols like VNC
• Added support for additional SPICE functionality,
including:
– Vdagent
– clipboard sharing
– USB redirection

GRUB 2 Support of Xen Project PV Images
• In the past, Xen Project software required a custom
implementation of GRUB called pvgrub
• The upstream GRUB 2 project now has a build target
which will construct a bootable PV Xen Project
image
– This ensures 100% GRUB 2 compatibility for pvgrub
going forward

Indirect Descriptors for Block PV Protocol
• Modern storage devices work much better with
larger chunks of data
• Indirect descriptors have allowed the size of each
individual request to triple, greatly improving I/O
performance when running on fast storage
technologies like SSD and RAID
• This support is available in any guest running Linux
3.11 or higher (regardless of Xen Project version)

Improved kexec Support
• kexec allows a running Xen Project host to be
replaced with another OS without rebooting
– Primarily used execute a crash environment to collect
information on a Xen Project hypervisor or dom0 crash

• The existing functionality has been extended to:
– Allow tools to load images without requiring dom0
kernel support (which does not exist in upstream
kernels)
– Improve reliability when used from a 32-bit dom0
– kexec-tools 2.0.5 or later is required

Improved XAPI and Mirage OS support
• XAPI and Mirage OS are sub-projects within the Xen
Project written in OCaml
• Both are also used in XenServer
(see http://xenserver.org/) and rely on the Xen
Project OCaml language bindings to operate well
• These language bindings have had a major overhaul
– Produces much better compatibility between XAPI,
Mirage OS and Linux distributions going forward

Experimental Support for Guest EFI boot
• EFI is the new booting standard that is replacing
BIOS
– Some operating systems only boot with EFI
– Some features, like SecureBoot, only work with EFI

Improved Integration With GlusterFS
• You can find a blog post to set up an iSCSI target on
the Gluster blog here

Improved ARM Support
• A number of new features have been implemented:
• 64 bit Xen on ARM now supports booting guests
• Physical disk partitions and LVM volumes can now
be used to store guest images using xen-blkback (or
is PV drivers better in terms of terminology)
• Significant stability improvements across the board
• ARM/multiboot booting protocol design and
implementation
• PSCI support

Improved ARM Support (2)
• Same DMA in Dom0 even with no hardware
IOMMUs (not sure what the implications of this are)
• ARM and ARM64 ABIs are declared stable and
maintained for backwards compatibility
• Significant usability improvements, such as
automatic creation of guest device trees and
improved handling of host DTBs

Improved ARM Support (3)
• Adding new hardware platforms to Xen Project on
ARM has been vastly improved, making it easier for
Hardware vendors and embedded vendors to port
to their board
• Added support for the Arndale board, Calxeda ECX2000 (aka Midway), Applied Micro X-Gene Storm, TI
OMAP5 and Allwinner A20/A30 boards
• ARM server class hardware (Calxeda Midway) has
been introduced in the Xen Project OSSTest
automated testing framework

Early Microcode Loading
• The hypervisor can update the microcode in the
early phase of boot time
– The microcode binary blob can be either as a
standalone multiboot payload, or part of the initial
kernel (dom0) initial ramdisk (initrd)
– To take advantage of this use latest version
of dracut with --early-microcode parameter and on the
Xen Project command line specify: ucode=scan.
– For details see dracut manpage
and http://xenbits.xen.org/docs/unstable/misc/xencommand-line.html

Xen Project Futures

Still More Fun to Come…
• Xen Automotive
– Xen Project in the entertainment center of your car?

• XenGT
– Virtualized GPU support

• Even More ARM Support
– On your server, in your phone, wherever…

• PVH stability and performance
– The new hypervisor mode to get harder and faster

Questions?

Russell.Pavlicek@xxxxxxxxxxxxxx
Twitter: @RCPavlicek