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

Hot-plugging support ups availability

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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