Performance decreases in W2K8 R2 with Hyper-V role installed and certain Intel processors

Performance decreases in Windows Server 2008 R2 when the Hyper-V role is installed on a computer that uses Intel Westmere or Sandy Bridge processors.

Symptoms:

Consider the following scenario:

  • You have a Windows Server 2008 R2-based computer that has a large amount of physical memory and that has Intel Westmere or Sandy Bridge processors.

    For example, you have a computer that has Intel Xeon 5600 series processors and that has 48 gigabytes (GB) physical memory.

  • You install the Hyper-V role on the computer.

In this scenario, the performance of the computer may decrease.

For example, the following performance issues may be encountered:

  • The CPU usage is high and the server responds slowly when you copy large files on the computer. For example, you copy a 10-GB file.
  • The disk I/O performance of the virtual machines (VMs) is slow.
  • Windows takes a long time to start.

Cause:

This issue occurs because the hypervisor supports only eight variable range Memory Type Range Registers (MTRRs). Additionally, the hypervisor cannot access the additional variable MTRRs that are introduced on recent Intel processors. Therefore, some regions of system memory are set to the default Uncacheable memory type, and the performance of the computer significantly decreases.

Notes

  • MTRRs are processor model specific registers (MSRs) that control the default caching for ranges of physical memory.
  • Intel Westmere and Sandy Bridge processors introduce additional variable MTRRs to enable systems to use a large amount of memory.

Fix:

A supported hotfix is available from Microsoft. However, this hotfix is intended to correct only the problem that is described in this article. Apply this hotfix only to systems that are experiencing this specific problem.

If the hotfix is available for download, there is a “Hotfix download available” section at the top of this Knowledge Base article. If this section does not appear, submit a request to Microsoft Customer Service and Support to obtain the hotfix.

NoteIf additional issues occur or if any troubleshooting is required, you might have to create a separate service request. The usual support costs will apply to additional support questions and issues that do not qualify for this specific hotfix. For a complete list of Microsoft Customer Service and Support telephone numbers or to create a separate service request, visit the following Microsoft Web site:

http://support.microsoft.com/contactus/?ws=support (http://support.microsoft.com/contactus/?ws=support)

NoteThe “Hotfix download available” form displays the languages for which the hotfix is available. If you do not see your language, it is because a hotfix is not available for that language.

Prerequisites

To apply this hotfix, you must be running one of the following operating systems:

  • Windows Server 2008 R2
  • Windows Server 2008 R2 Service Pack 1 (SP1)

For more information about how to obtain a Windows Server 2008 R2 service pack, click the following article number to view the article in the Microsoft Knowledge Base:

976932 (http://support.microsoft.com/kb/976932/ ) Information about Service Pack 1 for Windows 7 and for Windows Server 2008 R2

Registry information

To use the hotfix in this package, you do not have to make any changes to the registry.

Restart requirement

You must restart the computer after you apply this hotfix.

Hotfix replacement information

This hotfix does not replace a previously released hotfix.

Download this hotfix

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