The focus of Xen 4.6 is improving overall security of virtual environments, upgrading network performance and making it easy to migrate virtual machines from one version of the technology to another. Here’s what the project has to say about Xen 4.6:
Enables a new class of security applications: A number of significant improvements to Xen’s Virtual Machine Introspection (VMI) subsystems make it the best hypervisor for security applications. Hardware support for VM Functions (VMFunc) available on Intel’s 4th generation Haswell CPUs and Atom Silvermont CPUs decreases overheads. Support for Virtualization Exceptions is now available on Intel’s 5th generation Broadwell CPUs and Atom Goldmont CPUs has significantly reduced latency. VMI support for ARM CPUs has also been added.
Major improvements to scalability: Finer-grained grant table locks lead to significant scalability improvements in the Xen Project. For example, aggregate intrahost network throughput has improved more than 100% in some cases. In addition, byte-range locks were replaced with ticket locks, which have better fairness properties than previously used locks for improved scalability.
Redesign of live migration components to better support high availability: The Xen Project Hypervisors Live Migration subsystem implemented its second version (Migration v2) to be more robust, extensible and able to handle next-generation infrastructures. It has been tested by several vendors to ensure it is enterprise-ready. The updates provide better performance for 64 bit systems and add support for cross-bitness migration between 32 and 64 bit hosts. Migration v2 is optimized for PVH and Coarse-grained Lock-stepping (COLO), which will be fully integrated with Xen in the next release. In addition, Page Modification Logging (PML) was implemented for Intel CPUs, improving SpecJBB performance by 7.6% in log dirty mode.
Better quality: During the Xen 4.6 release cycle, the Xen Project increased its integration test capability by creating CI loops for Xen Hypervisor and OpenStack testing. Besides running tests on more hardware configurations, the number of test cases nearly doubled during the 4.6 release cycle, contributing to the best quality release yet. This is also reflected in test results by 3rd party vendor test suites, which are regularly run on the Xen Project codebase.
ARM support: The new release increases the maximum number of supported VCPUs for 64-bit ARM CPUs from 8 to 128 and adds support for 32-bit userspace applications to 64-bit guests. Additionally, new IP blocks, firmware interfaces and platforms are supported, such as non-PCI passthrough support, OVMF for ARM and GICv2 on GICv3 support. During the hardening phase of Xen 4.6, members of the Xen Project community closely collaborated with the CentOS Virtualization SIG to build and test Xen 4.6 packages for CentOS 7’s 64-bit ARM variant and tested it against OpenStack using libvirt.
Updates for automotive and embedded systems: The new release added support for two platforms targeting the embedded and automotive market segments: Xilinx Zynq® UltraScale+™ MPSoC and support for the Renesas R-Car Gen2 SoCs.
Intel Platform QoS Technologies for improved scalability and performance: Intel® Cache Allocation Technology (CAT) and Memory Bandwidth Monitoring (MBM) are included, which build on the Cache Monitoring Technology (CMT) introduced in Xen 4.5. CAT allows system administrators to assign more L3 cache capacity to individual VMs, resulting in lower latency and higher performance for high-priority workloads such as NFV, real-time and video-on-demand applications. MBM allows system administrators to identify memory bandwidth saturation on a Xen host that may be caused by several memory-intensive VMs running on the same host. Taking corrective actions, such as migrating VMs to a different Xen host, increases scalability and performance in the data center.
Xen is an important virtual machine software, or hypervisor, technology. It is the foundation for Citrix’s XenServer and Oracle’s Oracle VM products. It is also included in nearly every Linux distribution.
When Xen first appeared it was one of the first virtual machine technologies available for X86 architecture systems. Later, when Intel and AMD added special machine instructions to facilitate server and client virtualization, Xen was enhanced to support them. Xen 4.6 appears to be a mature platform that should support just about any workload.
As other microprocessors have emerged as important, the project has moved to make Xen available on them as well.
Xen faces a great deal of competition from technology offered by VMware, Microsoft and KVM, another open source project. Red Hat and IBM, for example, have moved to emphasize KVM rather than Xen, even though they both continue to support Xen.
Now that the race is underway, this release is unlikely to convince enterprises to move away from VMware, Microsoft or KVM-based virtual environments. It does, however, mean that dedicated Xen users will see improved security, performance and manageability.