Quoting from ZDNet:
“As we build future implementations, we’re making things perform better within the constraints of the architectural foundation, but without requiring software changes. Then we’re also extending the architecture,” Richard Uhlig, senior principal engineer at Intel, said during an interview at the Intel Developer Forum.
One planned improvement is a feature called extended page tables, an idea similar to an AMD virtualization technology called nested page tables. Both technologies speed up a facet of virtual machines dealing with memory.
In a computer without virtual machines, the operating system expects memory addresses to start at zero and work their way upward. But with many virtual machines sharing a computer’s memory, zero isn’t the starting place, and memory addresses skip from one patch to another, Uhlig said.
Consequently, one important job of a hypervisor is “page table shadowing,” which translates a virtual machine’s memory addresses to the real ones used by the actual computer. The more translation is required, the slower the virtual machine runs, and with programs such as databases that constantly switch among different patches of memory, the performance penalty can be anywhere from 10 percent to 25 percent, Uhlig said.
New versions of VT will get a feature called the page table walker, in which the processor rather than the hypervisor keeps track of that memory issue, he said. The overhead imposed “doesn’t drop to zero,” but will be much faster than the software-based function, Uhlig said.
But more sophisticated changes to networking are farther off because they require changes to the PCI standard that network cards and many other add-on devices use. For example, one idea that Intel plans to support is the splitting of a network card’s capacity among different virtual machines.
Work is under way at the PCI Special Interest Group to add features that will permit such splitting, said Rajesh Sankaran, an Intel senior staff researcher. The new specification is due later this year, and the first products supporting it are expected in 2007, he said.
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