This is a repost from Arianna’s blog, which contains a lot of in-depth technical articles related to the Xen Project.
The Xen Project Developer Summit
Linux x86 co-maintainer David Vrabel provided a status update on the newest features added to Linux domain support and set up a wishlist for future features to be developed. During the keynote session I had the chance to meet a former Xen Project intern, Elena Ufimtseva, who worked on the implementation of vNUMA in Xen during the 2013 OPW round, mentored by Citrix Senior Engineer Dario Faggioli. She also presented her work in 2013 at the Xen Developer Summit. I could gather details and her opinion about her experience with OPW and in finding a job after the end of the internship, and I could discuss with her some of the challenges experienced by an intern and the best ways to exploit those difficult aspects by turning them into stronger development skills.
The following talks provided in-depth details on the main research aspects of Xen development. Some of them covered the performance of Xen with respect to networking, such as Jun Nakajima‘s talk on the main bottlenecks found while experimenting with Xen as a Network Virtualization Functions platform component and the solutions that were implemented by Intel. Other talks focused on storage, as Felipe Franciosi‘s insight on memory grant technologies available in Xen that can contribute to optimising aggregate workloads of several GB/s per guest (he actually allowed me to take part in the BoF session that followed his talk, therefore giving me the chance to hear further opinions and learn even more on the storage performance achieved by Xen guests). Still on the same trend, Filipe Manco presented NEC Europe’s work towards tracking down performance limitations and bottlenecks that increase startup latencies of Xen guests, when they are run in bursts of thousands; he also proposed a prototype reimplementation of some Xen components to prove his points. Anil Madhavapeddy showed the benefits of the new Irminsule distributed transactional filesystem, that allows to handle storage accesses in a version control system fashion, letting unikernels running in isolated stubdomains, such as MirageOS, use a common and consistent API. More talks covered security aspects of virtualization, as Mihai Dontu‘s presentation, that proposed a zero-footprint implementation of memory introspection for Xen domUs that can allow a supervisor domain to perform run-time detection of malware on Xen-based guests; James Bielman described Galois’ implementation of Mandatory Access Control for the Xenstore, showing how it can be managed by a centralized security server as it does not benefit from the XSM security policy. James Fehlig‘s talk, instead, covered the important topic of virtualization management tools, providing an overview of libvirt, a status update on the libxenlight driver and a roadmap proposal. Moving on to the topic of architecture and hardware support, Daniel Kiper approached the subject of EFI, outlining how Xen efficiently uses its infrastructure and what can be improved in the support provided by the hypervisor. Wei Liu instead described the status of vNUMA support in Xen, giving an in-depth report of its implementation and of its importance with relevant statistics.
The main session opened with a detailed overview of the Verizon Cloud architecture provided by Don Slutz, which described what features are used and the optimization it provides to both Xen and QEMU. It also featured a report on the Linux kernel delta that SUSE supports for Xen and a proposal on how to address it, delivered by Luis Rodriguez. Following another trend were some Xen-on-ARM-related talks, as the presentation by Stefano Stabellini, that provided an insight on the current state of the project and how it performs on the newest ARMv8 64-bit platforms, and the one by Julien Grall, which detailed the process of porting an OS as a Xen-on-ARM guest. Jonathan Daugherty also described, in his talk, his experience in porting FreeRTOS to Xen on a Cortex A15-based platform. More talks were performance-related, as Zoltan Kiss‘ presentation on network improvements made in XenServer and Feng Wu‘s on Intel’s work on introducing interrupt posting with its virtualization technology. John Else explained his work about efficient inter-domain communication of performance data, his findings about the XenStore being the bottleneck in the current technique and proposed a lock-free, efficient solution to the issue. Talks also included the relevant topic of testing for a software ecosystem as complex as the Xen one: Ian Jackson presented Xen’s automatic testing facility, osstest, outlining its last development steps and the wider set of configurations it now supports. Some of the talks were related, instead, to safety aspects of using Xen in an environment with real-time constraints. Nathan Studer and Robert VanVossen presented DornerWorks’ efforts on certifying Xen for automotive, medical and avionics, the challenges behind the task, a proposed roadmap to overcome the most tricky aspects and the current state of the project. Sisu Xi described the Washington University’s work on RT-Xen with the aim of combining real-time and virtualization. Willing to give, instead, a more detailed insight on unikernels, Adam Wick outlined their features and described the general rules that establish whether a unikernel is the right choice for a software infrastructure component. Glauber Costa introduced the topic of LibraryOSs, highlighting their benefits in terms of performance, lightness and scalability, describing which applications they support and how can prove to be useful to the Xen community. Philip Tricca explained the drawbacks of the static configuration used to isolate system components in OpenXT, a collection of hardened Linux-on-Xen virtual machines providing a user platform for client devices, and a new toolkit to enhance the platform’s flexibility.
During the main session I met some of my fellow OPW interns. I had the chance to talk to the brilliant Mindy Preston, who worked on MirageOS’s network stack fixing bugs and implementing missing RFCs, about her experience and exchange opinions about ARM-based boards. I had the chance to take part in the final OPW/GSoC-related panel with her; it also featured the very professional GSoC intern Jyotsna Prakash, who worked on cloud API support for MirageOS by implementing cloud API bindings for OCaml, along with some of our mentors and Lars Kurth as a host. The panel gave us interns the chance to provide feedback to our mentors and to the program’s organization and to express our opinion about what we learned from it. It also covered very important aspects of participating in a large open-source project within a heterogeneous and just as big community: George Dunlap thoroughly explained the lights and shadows of Linus Torvalds’ approach to commenting bad code, while Konrad Wilk delivered a thoughtful insight about how cultural differences can influence the interaction between developers during software review.
What Did I Learn
Being able to attend the conference was a highly educational experience. It allowed me to get a better idea of how the community is organized, to get involved even more and hear about the experience of other attendees. I also could benefit from my mentor’s advice on how to interact with other developers. Having to speak in front of an audience also has always been one of the aspects of working on a project that I feared the most; the chance to take part in the panel and my mentor’s very useful advice make a huge addition to my experience and will allow me to fully exploit the opportunity to share my findings and my enthusiasm with others on future occasions.
As a final note, I’d like to thank my very patient mentor, Konrad Wilk, for allowing me to take part in OPW (even if I applied to him as a candidate on the very last day before the deadline) and for his invaluable guidance during the program; I’d like to thank also the GNOME Foundation and Xen Community Manager Lars Kurth for granting me the opportunity to attend the conference, and Elena Ufimtseva for giving me the benefit of her own experience. Last, but not least, I’d like to thank my always so helpful advisor, Paolo Valente, and Citrix Senior Engineer Dario Faggioli for introducing me to the internship program.