Last month Edinburgh was host to the latest Xen Project Developer Summit. For those who attended, and for those who couldn't make it this time, the session recordings and presentations have just been posted. The event saw content ranging from Xen on ARM and Xen in automotive infotainment, through to deeper discussions on fault tolerant system design and video display handling from a significant number of non-Citrix presenters. Of course there were several XenServer related sessions, and I'm including the abstracts and links for them below.
"Unlimited" Event Channels
David Vrabel, Citrix
Event Channels are Xen's mechanism for paravirtualized interrupts. These were limited to only 4096 which then limits the number of guests that a host may support to around 300 to 500. This presentation will give a brief introduction to event channels, a detailed look at the new, innovative FIFO-based event channel ABI that increases the limit to over 100,000 as well as having several other useful features (e.g., multiple priorities). Some of the key performance measurements of the new ABI will be shown.
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Test-as-a-Service and XenRT
Alex Brett, Citrix
In this presentation, Alex Brett will show how Citrix has constructed a Test-as-a-Service environment which is used by the wider XenServer engineering team, highlighting the benefits the approach provides, together with an introduction to the (recently open sourced) XenRT automation framework which powers it, and discuss how this could be applied within the Xen Project community.
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Increasing XenServer's VM Density
Jonathan Davies, Citrix
As the number of CPU cores in server-class hardware increases, the demand on a virtualisation platform increases for greater VM density. Most commercial virtualisation platforms now support several hundred VMs per host. This talk will describe the scalability challenges that were overcome in Citrix XenServer 6.2 to enable support for up to 500 fully virtualised or 650 paravirtualised VMs per host. These include limits with event channels, blktap, xenstored and consoled. It will also discuss how dom0 CPU utilisation was reduced in order to make a large number of VMs responsive and thus usable, and will present benchmark measurements quantifying these improvements.
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Open Source Citrix Windows PV Drivers
Paul Durrant, Citrix
Citrix has recently spent several months making sure all the key parts of XenServer are open source. Part of this effort made the XenServer Windows Paravirtual (PV) drivers available in source form under a BSD 2 clause license on GitHub. Building these drivers outside of the internal Citrix XenServer build environment was quite hard and the resulting binaries would only run correctly in a XenServer host environment. I have recently spent many weeks modifying the drivers so that they should work on any recent upstream Xen host environment thus making it much easier for anyone outside of Citrix to build and deploy the drivers. I would therefore like to give a brief tour of all the drivers, their source, what each of them does, and how they all interact. I will also discuss plans for posting signed versions of these drivers onto Windows Update for general use by the community.
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xenserver-core: What it is, How it is Built and How to get Involved
Euan Harris, Citrix
XenServer is open source and freely available, but it is packaged as an appliance image which must be installed on dedicated hardware. xenserver-core repackages the core components of XenServer so they can easily be built and installed on a standard Linux distribution. Its main goals are: * to make it easy to download, modify and build XenServer components, or just learn how they work; * to help upstream distributions to include up-to-date XenServer packages; * to provide an environment for experimentation. This talk will explain the motivations behind xenserver-core and how it relates to the open-sourcing of XenServer. For developers, it will cover how to get the code, how to build it and how to contribute back to the project. For packagers, it will explain the project's development and release processes and what an upstream maintainer can expect from it.
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SecureServe: A Multi-level Secure Server Virtualization Platform on Xen
Jason Sonnek, Adventium Labs
Due to the rapid shift toward cloud computing, virtual desktop infrastructure (VDI) and thin client computing, many organizations in the government desire a high assurance, multi-level secure server virtualization platform that is low-cost, open and enterprise ready. In this presentation, Jason Sonnek will present SecureServe, a recently launched effort to develop such a platform by building on the open-source Citrix XenServer. The SecureServe project will draw upon research in a number of areas, including dom0 disaggregation, Xen Security Modules mandatory access controls and static/dynamic attestation. In this presentation, Jason will describe the project objectives and requirements, the project's relation to Citrix XenClient XT and XenServer Windsor, current development status and plans for moving forward.
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Delivering Continuous Deployment of Xen-API at Cloud Scale
John Garbutt, Rackspace
Currently xen-api is really only installed today as part of XenServer. It has traditional enterprise style releases, with controlled upgrades and hotfixes when required. When deploying OpenStack Rackspace, with the help of the OpenStack community, have adopted an approach where any check-in could be deployed, and the system upgraded, from any other checkin from that last release, or earlier in the current release. It would be interesting to see if xen-api could move towards a model. At a minimum having more regular check points where an upgrade would be possible. When running a cloud, a very small amount of control plane downtime is possible, but ideally there should be zero downtime for user's virtual machines. We should explore the ability to only upgrade Xen as a last resort, but still be able to update as much the control and data plane as possible, while keeping VMs alive.
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Multiple Device Emulators for HVM Guests
Paul Durrant, Citrix
Currently Xen only allows a single device emulator to be attached to each HVM guest in a system and, to date, this has been QEMU generally running as a process in the same domain as the toolstack, or in a stub domain. To enable the deployment of virtual GPUs to HVM guests in XenServer, patches were created to allow multiple device emulators to be attached to each HVM guest. QEMU continues to be used to emulate the majority of the devices, but a second process is spawned to handle the virtual GPU. This opens up the possibility of the GPU vendors supplying 'appliance' driver domains in future. I'd like to give an overview of the changes that we've made to Xen and QEMU to enable the use of multiple emulators, the potential benefits to driver domains, plus the knock on effect of emulator disaggregation on the 'unplug' protocol and what we could do about this.
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Xen and XenServer Storage Performance
Felipe Franciosi, Citrix
The development of low latency storage media such as modern Solid State Drives (SSD) brings new challenges to virtualisation platforms. For the first time, we are witnessing storage back ends which are so fast that the CPU time spent in processing data significantly impacts the delivered throughput. This is aggravated by CPU speeds remaining largely constant while storage solutions get faster by orders of magnitude. To meet user demands and fully exploit SSD performance under Xen, new technologies are necessary. This talk will discuss the Xen storage virtualisation data path when using various back ends (e.g. blkback, tapdisk, qemu). It will explain why it is hard to exploit SSD performance with current technologies and present measurement data for a variety of workloads. Finally, it will show how techniques such as persistent grants and indirect I/O can help to mitigate the problem.
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