A Windows Server 2008 R2-based computer that has some NUMA-based processors and more than 256 logical processors runs in SMP mode as a 64-processor system and may experience decreased performance

Consider the following scenario:

• You have a Windows Server 2008 R2-based computer that has some non-uniform memory access (NUMA)-based processors.
• The system has more than 256 logical processors.

In this scenario, you experience the following issues after you start the system:

• The number of logical processors is changed to 64.
• The NUMA feature is disabled, and the operating system runs in symmetric multiprocessor (SMP) mode.
• The performance of the computer decreases significantly.

Consider the following sample scenario:

• You install Windows Server 2008 R2 on a computer that has some Intel Westmere-EX processors.
• The computer has 16 10-core Intel Westmere-EX processors that have Hyper-Threading enabled.
  
  Note The computer has the equivalent of 320 logical processors.

In this scenario, the operating system starts as a 64-processor SMP system.

The issue occurs because Windows Server 2008 R2 incorrectly forces a NUMA-based computer to become a SMP computer if the number of logical processors is greater than 256.

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 website: Note 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). 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:

Registry information

To use the 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 0.16xxx	Windows Server 2008 R2	RTM	GDR
  6.1.760 0.20xxx	Windows Server 2008 R2	RTM	LDR
  6.1.760 1.17xxx	Windows Server 2008 R2	SP1	GDR
  6.1.760 1.21xxx	Windows Server 2008 R2	SP1	LDR

• GDR service branches contain only those fixes that are widely released to address widespread, critical issues. LDR service branches contain hotfixes in addition to widely released fixes.
• 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 very important for maintaining 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

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

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

Additional file information

Additional file information for Windows Server 2008 R2

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