Monthly Archives: March 2014

Rackspace hosts Xen Project Hackathon, May 29-30 in London

I am pleased to announce the next Xen Project Hackathon. The Hackathon will be hosted by Rackspace in their London offices, May 29 and 30. I wanted to thank Paul Voccio and Gus Maskowitz from Rackspace for hosting the Hackathon. I also wanted to thank Rackspace for hosting the Xen Project wiki, mailing lists, blog and other services. This is in line with Rackspace’s vision of openness and helping people:

At Rackspace we build and live openness as much as possible and go out of our way to support and nurture open source where we can. We help people achieve success by solving their hybrid hosting and cloud problems. In that same line we are proud to help the Xen Project run a successful Hackathon in London 2014. Rackspace

What to expect at a Xen Project Hackathon?

The aim of the Hackathon is to give developers the opportunity to meet face to face, to discuss development, coordinate, write code and collaborate with other developers. Of course the event will allow everyone to meet in person and build relationships: to facilitate this, we will have a social event on the evening of the 29th. We will cover many hot topics such as the latest Xen Project Hypervisor 4.4 features, planning for the next Xen Project Hypervisor release, Cloud Integration, Cloud Operating Systems, Mirage OS, Xen Project in emerging segments such as embedded, mobile, automotive and NFV. But at the end of the day, the community will chose the topics that are covered.

To ensure that the event runs efficiently, we are following the following process: Each day is divided into several segments. We will have a number of work areas that are labelled with numbers (or other unique identifiers). Each morning starts with a plenary and scheduling session. Every attendee who cares about a topic can announce a topic, which we will map against a work area and time-slot. This makes it easy for other attendees to participate in projects and discussions they care about. Of course we also encourage attendees to highlight projects they plan to share before the event by adding them to our wiki.

We will wrap up each day with another short plenary session: the aim of this session is to summarize what was done, show brief demos and make improvements to the process.

To give you a sense of the venue, we attached a few pictures of the venue and past events:

Rackspace_events_2 MA0139_N73_medium MA0139_N60_medium
MA0139_N10_medium Rackspace_events_1 MA0139_N94_medium

How to Register?

As spaces at the Xen Project Hackathon are limited, we are asking attendees to request an invitation. If you did, you will be notified by email within 5 business days with instructions on how to confirm your invitation.

Like last year, we will be asking for a small registration fee of $15. This fee will be given to a charity or open source organisation. You will need to cover your own travel, accommodation and other costs such as evening meals, etc. We do have limited travel stipends available for individuals who cannot afford to travel. Please contact community dot manager at xenproject dot org if you need to make use of it.

More Information

Xen Project Team Hits the Road

You’ll find many of our members and contributors taking on more than coding this spring. We’re excited to attend several upcoming industry events and share Xen Project milestones, news, use cases and roadmap updates in-person with many in our community.

We encourage you to attend any of these upcoming Xen Project talks. And, if you do, make sure to introduce yourself to the speaker.  It’s always good to meet new people from the Xen Project community!

First Stop: Linux Foundation Collaboration Summit

This week you’ll find the Xen Project team in wine country at the Linux Foundation Collaboration Summit in Napa Valley, California.  We have a terrific set of Xen Project sessions at this year’s conference. In fact, the schedule for March 27 reads like a mini Xen Project Summit.

At 11:30 AM, GlobalLogic CTO Alex Azizam discusses “Xen versus Xen Automotive,” an overview of the technologies required to fully use Xen Project software in automotive applications.

At 2:00 PM, Intel Software Engineer Zhiyuan Lv presents “XenGT: A Full GPU Virtualization Solution with Mediated Pass-Through.”  GPU virtualization is especially hot right now, and this project to provide high-performance virtual GPUs for use within the Xen Project environment is especially interesting.

At 3:00 PM, Oracle Software Engineer Mukesh Rathor talks about “PVH: A PV Guest in HVM Container.”  The combination of PV and HVM promises to yield the highest performance of any Xen Project hypervisor mode for most workloads.

And, finally, at 4:00 PM, I deliver an overview of our new release with “Xen Project 4.4: Features and Futures.”  Attendees will hear about the newest capabilities, as well as hear a quick summary of some upcoming enhancements on the project roadmap.

Check out the Collaboration Summit Q&A on for more event highlights and Xen Project reflections.

Up Next: ApacheCon / CloudStack Collaboration Conference / CentOS Dojo

With barely any time to rest, you’ll next find us at ApacheCon and the CloudStack Collaboration Conference April 7-9 in Denver, Colo.

At 2:20 PM on Thursday, April 10 I’ll again present “Xen Project 4.4: Features and Futures” for the Apache CloudStack enthusiasts visiting the Mile High City.

Later that day, at 4:20 PM I’ll deliver “Using and Understanding Xen CentOS” at CentOS Dojo (also co-located with ApacheCon), discussing how to use the Xen Project hypervisor on top of CentOS.

On Friday, April 11 at 11:45 AM, John Mark Walker, Gluster Community Manager at Red Hat, presents “The New Cloud Stack — CloudStack, Xen and GlusterFS” and the latest work from Gluster engineers to improve integration and scalability across these technologies.

More to Come…

If we miss you in California or Colorado, be sure to visit and check out the upcoming events to find out when a Xen Project talk is coming to a conference near you.  And don’t forget that we normally link to our talk slides and videos as they become available.

Hope to see you at an event soon!

XenGT – a Full Graphics Virtualization Solution on Intel ® Processor Graphics


The Graphics Processing Unit (GPU) has become a fundamental building block in today’s computing environment, accelerating tasks from entertainment applications (gaming, video playback, etc.) to general purpose windowing (Windows* Aero*, Compiz Fusion, etc.) and high performance computing (medical image processing, weather forecast, computer aided designs, etc.).

Today, we see a trend toward moving GPU-accelerated tasks to virtual machines (VMs). Desktop virtualization simplifies the IT management infrastructure by moving a worker’s desktop to the VM. In the meantime, there is also demand for buying GPU computing resources from the cloud. Efficient GPU virtualization is required to address the increasing demands.

Enterprise applications (mail, browser, office, etc.) usually demand a moderate level of GPU acceleration capability. When they are moved to a virtual desktop, our integrated GPU can easily accommodate the acceleration requirements of multiple instances.

GPU Background

Let’s first look at the architecture of Intel Processor Graphics:


The render engine represents the GPU acceleration capabilities with fixed pipelines and execution units, which are used through GPU commands queued in command buffers. The display engine routes data from graphics memory to external monitors, and contains states of display attributes (resolution, color depth, etc.). The global state represents all the remaining functionality, including initialization, power control, etc. Graphics memory holds the data, used by the render engine and display engine.

The Intel Processor Graphics uses system memory as the graphics memory, through the graphics translation table (GTT). A single 2GB global virtual memory (GVM) space is available to all GPU components through the global GTT(GGTT). In the meantime, multiple per-process virtual memory (PPVM) spaces are created through the per-process GTTs (PPGTTs), extending the limited GVM resource and enforcing process isolation.

Graphics Virtualization Technologies

Several technologies achieve graphics virtualization, as illustrated in the image below, with more hardware acceleration toward the right.


Device emulation is mainly used in server virtualization, with emulation of an old VGA display card. Qemu is the most widely used vehicle. Full emulation of a GPU is almost impossible, because of complexity and extremely poor performance.

API forwarding implements a frontend/backend driver pair. The frontend driver forwards high-level DirectX/OpenGL API calls from the VM to the backend driver in the host through an optimized inter-VM channel. Multiple backend drivers behave like normal 3D applications in the host, so a single GPU can be multiplexed to accelerate multiple VMs. However, the difference between the VM and host graphics stacks easily leads to reduced performance or compatibility issues. Because it is hardware-agnostic, this is the most widely used technology, so far. Actual implementations vary, depending on the level where forwarding happens. For example, VMGL directly forwards GL commands, while VMware vGPU presents itself as a virtual device, with high-level DirectX calls translated to its private SVGA3D protocol. Another recent example is Virgil, with its experimental virtual 3D support for QEMU.

Direct pass-through, based on VT-d, assigns the whole GPU exclusively to a single VM. When achieving the best performance, it sacrifices the sharing capability.

Mediated pass-through extends direct pass-through, using a software approach. Every VM is allowed to access partial device resources without hypervisor intervention, while privileged operations are mediated through a software layer. It sustains the performance of direct pass-through, while still provides the sharing capability. XenGT adopts this technology. 


XenGT is a full GPU virtualization solution with mediated pass-through, on Intel Processor Graphics. A virtual GPU instance is maintained for each VM, with part of performance critical resources directly assigned. The capability of running native graphics driver inside a VM, without hypervisor intervention in performance critical paths, achieves a good balance among performance, feature and sharing capability.


Above figure shows the overall XenGT architecture. Each VM is allowed to access a partial performance critical resource without hypervisor intervention. Privileged operations are trapped by Xen and forwarded to the mediator for emulation. The mediator emulates a virtual GPU instance for each VM. Context switches are conducted by the mediator when switching the GPU between VMs. XenGT implements the mediator in dom0. This avoids adding complex device knowledge to Xen, and also permits a more flexible release model. In the meantime, we want to have a unified architecture to mediate all the VMs, including dom0, itself. So, the mediator is implemented as a separate module from dom0’s graphics driver. It brings a new challenge, that Xen must selectively trap the accesses from dom0’s driver while granting permission to the mediator. We call it a “de-privileged” dom0 mode.

Performance critical resources are passed through to a VM:

  • Part of the global virtual memory space
  • VM’s own per-process virtual memory spaces
  • VM’s own allocated command buffers (actually in graphics memory)

This minimizes hypervisor intervention in the critical rendering path. Even when a VM is not scheduled to use the render engine, that VM can continuously queue commands in parallel.

Other operations are privileged, and must be trapped and emulated by the mediator, including:

  • PCI configuration registers
  • GTT tables
  • Submission of queued GPU commands

The mediator maintains the virtual GPU instance based on the traps mentioned above, and schedules use of the render engine among VMs to ensure secure sharing of the single physical GPU.

Current Status

The latest source codes and the setup guide are available at the github repositories:

(The first repository has a XenGT_Setup_Guide.pdf, which supplies step-by-step instructions for getting a system set up.)




Patches are welcomed!

We plan to upstream this work, and are now preparing some cleanup.



XenGT was first announced in Sep 2013:

It was presented at the 2013 Xen Project Developer Summit, Edinburgh:

An update was announced recently in Feb 2014:

Xen 4.4 Released is pleased to announce the release of Xen 4.4.0. The release is available from the download page:

Xen 4.4 is the work of 8 months of development, with 1193 changesets. It’s our first release made with an attempt at a 6-month development cycle. Between Christmas, and a few important blockers, we missed that by about 6 weeks; but still not too bad overall.

Additionally, this cycle we’ve had a massive increase in the amount of testing. The XenProject’s regression testing system, osstest, has recieved a number of additional tests, and the XenServer team at Citrix have put Xen through their massive testing suite (XenRT). Additionally, early in this development cycle we had the go-ahead to use Coverity static analysis engine to comb through the source code for hard-to-spot bugs. The result should be that Xen 4.4 is one of the most secure, reliable releases yet.


Although the development part of the release cycle was shorter than the previous one, we still have far too many exciting improvements than we can mention in this blog post; I’ll call out just a few.

Probably one of the most important is solid libvirt support for libxl. Jim Fehlig from SuSE and Ian Jackson from Citrix worked together to test and improve the interface between libvirt and libxl, making it fast and reliable. This lays the foundation for solid integration into any tools that can use libvirt, from GUI VM managers to cloud orchestration layers like CloudStack or OpenStack.

Another big one is a new scalable event channel interface, designed and implemented by David Vrabel from Citrix. The original Xen event channel interface was limited to the number of bits on the platform squared — 1024 for 32-bit guests and 4096 for 64-bit guests. With many VMs requiring 4 event channels each, that means a theoretical maximum of 256 guests on a 32-bit dom0 — more than enough back when a large machine had 8 cores, and every VM was a full OS; but a major limitation on systems with 128 cores, or those using cloud OSes like Mirage or OSv. The new “FIFO” event channel interface by default scales up to over 200,000 event channels, and in the future can be extended even further if necessary in a backwards-compatible manner. This should be enough for many years to come.

The ARM port is maturing quickly. As of 4.4, the hypervisor ABI for ARM has been declared stable, meaning that any guest which uses the 4.4 ARM ABI can rely on being able to boot on all future versions of Xen. There are a number of improvements making Xen on ARM more flexible, easier to set up and use, and easier to extend to new platforms. More details can be found in the Xen 4.4 feature list.

One other feature worth a note is Nested Virtualization on Intel hardware. It’s not ready for production use yet, but it has improved to the point where we feel comfortable moving it from “experimental” to “tech preview”. Please feel free to take it for a spin and report any issues you find.

There are many more improvements and changes under the hood. For a more complete list, see the Xen 4.4 feature list.

Features in related projects

The Xen Project is part of a much larger ecosystem of projects. We are typically very closely tied to Linux and qemu, but a number of other projects have had important developments that are worth a mention.

The first is the pv port of grub2. Rather than having a re-implementation of grub in the Xen tree, grub2 now has native support for running in Xen and using the Xen pv block protocol. This guarantees 100% compatibility with grub2 going forward.

Another project worth a mention is the 3.3 release of Xen Orchestra. Xen Orchestra is a web interface that interfacer with the xapi protocol (and thus can be used for XCP, XenServer, or other xapi-based systems). New creating snapshots, revert or delete, remove host from pool, restart toolstack/reboot/shutdown host) and more stable upgrade process from appliance

Finally, GlusterFS 3.5 now supports creating iSCSI nodes. One of the benefits of this is that now, by creating iSCSI devices in dom0, Xen guest disks can be stored in GlusterFS.


Xen Project Developer Summit Call for Participation is Open

Join us in Chicago August 18-19, 2014

The Xen Project Developer Summit will feature content for developers, integrators and power users of the Xen Project. We are looking for presentations related to development, such as development proposals, updates on feature development, project updates, etc. We are also looking for insight into best practices in deploying Xen Project at scale, case studies by Xen users and other topics that large scale users of the Xen Project hypervisor care about.

The program committee will be looking for presentations and workshops related to working with the Xen Project. Topics related to Xen Project development include:

  • development proposals
  • updates on feature development
  • project updates
  • discussions and proposals on the architectural evolution of Xen Project
  • development best practices
  • studies and benchmarks of system characteristics such as performance/scalability/security/ease of use/power consumption
  • lessons learned
  • interfacing with other open source projects
  • making Xen Project software easier to consume by distributions and integrators

We are also interested in proposals that provide insight into best practices in deploying Xen Project, case studies by Xen Project users and other topics that large users and integrators of Xen Project care about. This includes:

  • deploying Xen Project software or its sister projects at scale
  • best practices for working with Xen Project
  • case studies by users
  • Xen Project benchmarks
  • tips and tricks in securing Xen-Project-based clouds
  • managing Xen-Project-based environments
  • open source projects that are related to Xen Project and deliver benefits to our users
  • 3rd party integrations
  • and more!

In short, if it’s relevant to Xen Project development, integration and usage we are interested in what you might have to say.

Submit Your Talk Proposal by May 2

Ready to submit your talk, or just interested in learning more?  Click here.