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AMD Introduces Quad-Core Opteron Processor »

Virtualization

New features of the Barcelona supporting virtualization:

  • Rapid Virtualization Indexing (formerly Nested Page Tables, code name Trinity):
    This new technology in AMD Virtualization accelerates virtual-to-physical address translation functionality that was previously performed in the hypervisor software, by performing these functions in the memory controller within the CPU. Nested Paging allows the memory controller to manage the page tables in hardware, whereas the traditional Shadow Page Tables are managed by the hypervisor. By handling the extra layer of address translations introduced by virtualization in hardware, the complexity of memory management in virtualized environments is reduced, resulting in faster switching times between virtual machines.
    As long as Intel's memory controller is part of the separate Northbridge, Intel will not be able to incorporate similar technologies in its processors. Since virtualization is memory intensive, a shared Front-Side Bus (FSB) as Intel is using creates bottlenecks, AMD says.
    Nested Page Tables are supported by Novell SLES 10 SP1 and VMware ESX 3i. Microsoft, Red Hat, and Sun also announced support.
  • Tagged TLB (Translation Look-aside Buffer):
    The Tagged TLB specifies to which virtual machines memory pages are assigned. This allows more efficient switching between virtual machines, improving application reponsiveness. Since the relations between memory pages and virtual machines are administrated, no TLB flushes are needed.
    The current Intel Xeon processors, with their external memory controllers, have to flush the TLB each time another virtual machine is scheduled.
  • Device Exclusion Vector (DEV):
    The DEV is part of the memory controller and lets the hypervisor know whether a virtual machine is allowed to access a memory page or not, effectively isolating the virtual machines further, for tighter security.
    While the DEV allows security checks to take place in hardware, in Intel's CPUs these checks have to be done in software.
  • Extended Migration:
    This feature allows virtual machines to be live migrated over the full range of Opteron processors (compare Intel's VT FlexMigration).

Virtualization is Memory Intensive [AMD]

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