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The vast majority of Intel server chips of the Xeon E3, Xeon E5, and Xeon E7 product lines support VT-d. The first—and least powerful—Xeon to support VT-d was the E5502 launched Q1'09 with two cores at 1.86 GHz on a 45 nm process. [2]
In virtualization, guest operating systems can use hardware that is not specifically made for virtualization. Higher performance hardware such as graphics cards use DMA to access memory directly; in a virtual environment all memory addresses are re-mapped by the virtual machine software, which causes DMA devices to fail.
The Message Signaled Interrupts (MSI) feature of the PCI 2.2 and later specifications cannot be used without the local APIC being enabled. [8] Use of MSI obviates the need for an I/O APIC. Additionally, up to 224 interrupts are supported in MSI mode, and IRQ sharing is not allowed.
x86 virtualization is the use of hardware-assisted virtualization capabilities on an x86/x86-64 CPU.. In the late 1990s x86 virtualization was achieved by complex software techniques, necessary to compensate for the processor's lack of hardware-assisted virtualization capabilities while attaining reasonable performance.
FreeBSD 6.3 and 7.0 released in 2008 added support for MSI and MSI-X. [17] OpenBSD 5.0 released in 2011 added support for MSI. [18] 6.0 added support for MSI-X. [19] Linux gained support for MSI and MSI-X around 2003. [20] Linux kernel versions before 2.6.20 are known to have serious bugs and limitations in their implementation of MSI/MSI-X. [21]
Platform virtualization is performed on a given hardware platform by host software (a control program), which creates a simulated computer environment, a virtual machine (VM), for its guest software. The guest software is not limited to user applications; many hosts allow the execution of complete operating systems.
The virtualization introduces only a negligible overhead and allows running hundreds of virtual private servers on a single physical server. In contrast, approaches such as full virtualization (like VMware ) and paravirtualization (like Xen or UML ) cannot achieve such level of density, due to overhead of running multiple kernels.
A single physical PCI Express bus can be shared in a virtual environment using the SR-IOV specification. [1] [2] The SR-IOV offers different virtual functions to different virtual components (e.g. network adapter) on a physical server machine.