What is SLAT?
SLAT stands for "Second Level Address Translation".
Intel calls their SLAT technology EPT (Extended Page Table) . This technology was introduced in the Nehalem microarchitecture found in certain Core i7, Core i5, and Core i3 processors.
AMD, beginning with their third generation Opteron processors (code name Barcelona) support SLAT through their Rapid Virtualization Indexing (RVI) technology.
With respect to memory management, Windows Server 2008 R2 Hyper-V supports a new feature named Second Level Address Translation (SLAT). SLAT leverages AMD-V Rapid Virtualization Indexing (RVI) and Intel VT Extended Page Tables (NPT) technology to reduce the overhead incurred during virtual to physical address mapping performed for virtual machines. Through RVI or EPT respectively, AMD-V and Intel VT processors maintain address mappings and perform (in hardware) the two levels of address space translations required for each virtual machine, reducing the complexity of the Windows hypervisor and the context switches needed to manage virtual machine page faults. With SLAT, the Windows hypervisor does not need to shadow the guest operating system page mappings. The reduction in processor and memory overhead associated with SLAT improves scalability with respect to the number of virtual machines that can be concurrently executed on a single Hyper-V server. As an example, the Microsoft Remote Desktop Services (RDS) team recently blogged about performance tests conducted using an internal simulation tool on a Windows Server 2008 Terminal Services configuration running as a virtual machine on Windows Server 2008 R2 Hyper-V. The results showed that a SLAT-enabled processor platform increased the number of supported sessions by a factor of 1.6 to 2.5 when compared with a non-SLAT processor platform. Overall, Microsoft reports that with SLAT-enabled processors, the Windows hypervisor processor overhead drops from about 10% to about 2%, and reduces memory usage by about 1 MB for each virtual machine.
Although RVI is not required to support workloads running on Windows Server 2008 R2 Hyper-V, if you intend to run memory-intensive workloads like Remote Desktop Services, SQL Server, or web services, you should perform testing on SLAT-enabled platforms to determine whether or not you can gain significant performance improvements.
To find out if your processor supports SLAT, you will need to download a copy of CoreInfo from here