Xen 3.4.0 released with more client device, Hyper-V integration

Xen, the de facto virtualization hypervisor for Linux and the basis of Citrix's commercial products, has reached version 3.4.0 bringing improved support for client devices, integration with Microsoft's Hyper-V hypervisor, better reliability and power management, and many CPU-level big fixes.

Xen developer Keir Fraser announced the official release of Xen 3.4.0 on the project's mailing list, saying it contains a number of important new features and updates.

The hypervisor now supports CPU and memory “offlining” for better reliability, improved frequency/voltage controls and deep-sleep support, and its scheduler and timers have been optimised for peak power savings.

Also new is support for Microsoft's Hyper-V Enlightened I/O interface.

Sydney-based Xen developer Simon “Horms” Horman was involved with two improvements to PCI pass-through.

The new features allow any unused PCI slot to be used for PCI pass-through, including hot-plug, Horms wrote on his blog.

“Previously only slots six and seven could be used, limiting users to two pass-through devices per domU,” he said. “The new limit is around 28, as there are 32 possible slots on a PCI bus, and typically four are used by a domU for emulated devices.”

“Fewer devices will be available for pass-through if extra ioemu devices are attached to the domU.”

Horms said the new release also allows the user to specify the slot used for pass-through of devices attached to domU at boot time.

“This mirrors the ability to select the slot when a device is hot-plugged,” he said.

“Unfortunately there have also been a number of bugs in pass-through. Many of these have been fixed. But and as of the release a known problem is that domains can't be started if they have previously had PCI devices hot-plugged.”

To overcome this limitation, Horms recommends using the xm_pci_list_v3.patch and xm_pci_attach_v2.patch patches.

Xen can be downloaded from http://www.xen.org/download/.

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