Symptoms

Consider the following scenario:

  • You have a computer that uses a multicore processor and that is running Windows Server 2008 R2.

  • You install the Hyper-V server role on the computer, and then you run some virtual machines (VMs) on the computer.

  • The VMs process a heavy workload.

In this scenario, the CPU usage for the VMs reaches 100 percent. However, some CPU cores are idle on the host computer.

If you open Resource Monitor, Resource Monitor indicates that some CPU cores have a high workload and that other CPU cores are idle in a parked status.

Cause

This issue occurs because Power Manager does not unpark CPU cores correctly.

When Power Manager runs in the Hyper-V root partition, Power Manager reads two variables from a page that is shared with the hypervisor to calculate the idle time of a processor. However, Power Manager may read meaningless values because of a hypervisor interception. Therefore, the power manager calculates an incorrect idle time for the processor and does not unpark CPU cores correctly.

Resolution

Hotfix information

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 the problem described in this article. This hotfix might receive additional testing. Therefore, if you are not severely affected by this problem, we recommend that you wait for the next software update that contains this hotfix.

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, contact Microsoft Customer Service and Support to obtain the hotfix.

Note If 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=supportNote The "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 Windows Server 2008 R2 or Windows Server 2008 R2 Service Pack 1 (SP1). Additionally, you must have the Hyper-V server role installed.

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 Information about Service Pack 1 for Windows 7 and for Windows Server 2008 R2

Registry information

To use this hotfix, you do not have to change 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.

File information

The global version of this hotfix installs files that have the attributes that are listed in the following tables. The dates and the times for these files are listed in Coordinated Universal Time (UTC). The dates and the times for these files on your local computer are displayed in your local time together with your current daylight saving time (DST) bias. Additionally, the dates and the times may change when you perform certain operations on the files.

Windows Server 2008 R2 file information notes

Important Windows 7 hotfixes and Windows Server 2008 R2 hotfixes are included in the same packages. However, hotfixes on the Hotfix Request page are listed under both operating systems. To request the hotfix package that applies to one or both operating systems, select the hotfix that is listed under "Windows 7/Windows Server 2008 R2" on the page. Always refer to the "Applies To" section in articles to determine the actual operating system that each hotfix applies to.

  • The files that apply to a specific product, milestone (RTM, SPn), and service branch (LDR, GDR) can be identified by examining the file version numbers as shown in the following table:

    Version

    Product

    Milestone

    Service branch

    6.1.760
    0.20xxx

    Windows Server 2008 R2

    RTM

    LDR

    6.1.760
    1.21xxx

    Windows Server 2008 R2

    SP1

    LDR

  • The MANIFEST files (.manifest) that are installed for each environment are listed separately in the "Additional file information for Windows Server 2008 R2" section. MANIFEST files and the associated security catalog (.cat) files, are extremely important to maintain the state of the updated components. The security catalog files, for which the attributes are not listed, are signed with a Microsoft digital signature.

For all supported x64-based versions of Windows Server 2008 R2

File name

File version

File size

Date

Time

Platform

Ntoskrnl.exe

6.1.7600.20942

5,475,712

13-Apr-2011

05:26

x64

Ntoskrnl.exe

6.1.7601.21702

5,562,240

13-Apr-2011

05:14

x64

Ntkrnlpa.exe

6.1.7600.20942

3,967,872

13-Apr-2011

04:53

Not applicable

Ntoskrnl.exe

6.1.7600.20942

3,911,552

13-Apr-2011

04:53

Not applicable

Ntkrnlpa.exe

6.1.7601.21702

3,967,872

13-Apr-2011

05:59

Not applicable

Ntoskrnl.exe

6.1.7601.21702

3,912,576

13-Apr-2011

05:59

Not applicable

Workaround

To work around this issue, change the Power Plan setting to High Performance.

Status

Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.

More Information

For more information about software update terminology, click the following article number to view the article in the Microsoft Knowledge Base:

824684 Description of the standard terminology that is used to describe Microsoft software updates

Additional file information

Additional file information for Windows Server 2008 R2

Additional files for all supported x64-based versions of Windows Server 2008 R2

File name

Amd64_137aa4b49a07bf605b8313cdb7ec2281_31bf3856ad364e35_6.1.7600.20942_none_3ed3b2c5c570c2ff.manifest

File version

Not applicable

File size

699

Date (UTC)

13-Apr-2011

Time (UTC)

18:59

Platform

Not applicable

File name

Amd64_1a424780b6e69a0e155e51c62af3c2f2_31bf3856ad364e35_6.1.7601.21702_none_26a61d7f8c6bc47d.manifest

File version

Not applicable

File size

699

Date (UTC)

13-Apr-2011

Time (UTC)

18:59

Platform

Not applicable

File name

Amd64_284971b7f7169c17834dd846c9ac9664_31bf3856ad364e35_6.1.7600.20942_none_d827b4bbccfe0cba.manifest

File version

Not applicable

File size

1,042

Date (UTC)

13-Apr-2011

Time (UTC)

18:59

Platform

Not applicable

File name

Amd64_2b6f61612d88969272cbe20462d18953_31bf3856ad364e35_6.1.7601.21702_none_a46af32443f56215.manifest

File version

Not applicable

File size

701

Date (UTC)

13-Apr-2011

Time (UTC)

18:59

Platform

Not applicable

File name

Amd64_4fde11903434148dc142c4cf75f8e555_31bf3856ad364e35_6.1.7600.20942_none_c6779f3e874d1e87.manifest

File version

Not applicable

File size

721

Date (UTC)

13-Apr-2011

Time (UTC)

18:59

Platform

Not applicable

File name

Amd64_e23c93acbf0430227b6d39e8b46e5188_31bf3856ad364e35_6.1.7600.20942_none_eefec27bbc3b767d.manifest

File version

Not applicable

File size

701

Date (UTC)

13-Apr-2011

Time (UTC)

18:59

Platform

Not applicable

File name

Amd64_e69ece584040201e82df0c5a824d190f_31bf3856ad364e35_6.1.7601.21702_none_ab5e2a616f61306f.manifest

File version

Not applicable

File size

1,042

Date (UTC)

13-Apr-2011

Time (UTC)

18:59

Platform

Not applicable

File name

Amd64_microsoft-windows-os-kernel_31bf3856ad364e35_6.1.7600.20942_none_c8d73862e6d3eed3.manifest

File version

Not applicable

File size

15,291

Date (UTC)

13-Apr-2011

Time (UTC)

06:24

Platform

Not applicable

File name

Amd64_microsoft-windows-os-kernel_31bf3856ad364e35_6.1.7601.21702_none_cae8d518e3d9eafb.manifest

File version

Not applicable

File size

15,291

Date (UTC)

13-Apr-2011

Time (UTC)

07:09

Platform

Not applicable

File name

Amd64_microsoft-windows-r..gistry-trustedtypes_31bf3856ad364e35_6.1.7600.20942_none_e0a4d0556118f96d.manifest

File version

Not applicable

File size

8,049

Date (UTC)

13-Apr-2011

Time (UTC)

06:02

Platform

Not applicable

File name

Update.mum

File version

Not applicable

File size

3,215

Date (UTC)

13-Apr-2011

Time (UTC)

18:59

Platform

Not applicable

File name

X86_microsoft-windows-os-kernel_31bf3856ad364e35_6.1.7600.20942_none_6cb89cdf2e767d9d.manifest

File version

Not applicable

File size

16,151

Date (UTC)

13-Apr-2011

Time (UTC)

05:21

Platform

Not applicable

File name

X86_microsoft-windows-os-kernel_31bf3856ad364e35_6.1.7601.21702_none_6eca39952b7c79c5.manifest

File version

Not applicable

File size

16,151

Date (UTC)

13-Apr-2011

Time (UTC)

06:37

Platform

Not applicable

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