XP Kernel Update for MultiCore CPUs

[Widkidone]

Thanks JRd1st (Tweaksrus.com)

The hotfix isn't very new, but the news if it is, at least to many of us.

SYMPTOMS
Computers that are equipped with multiple processors that support processor power management features, such as Advanced Configuration and Power Interface (ACPI) processor performance states, require Microsoft Windows XP Service Pack 2 (SP2). Additional updates are available to optimize performance and behavior on computers that are running Windows XP SP2. Without these updates, computers that are equipped with these power management-capable, mobile, dual-core processors may experience decreased performance or unexpected behavior.

SOLUTION
Possible decrease in performance during demand-based switching
Demand-Based Switching (DBS) is the use of ACPI processor performance states (dynamic voltage and frequency scaling) in response to system workloads. Windows XP processor power management implements DBS by using the adaptive processor throttling policy. This policy dynamically and automatically adjusts the processor’s current performance state in response to system CPU use without user intervention.

When single-threaded workloads run on multiprocessor systems that include dual-core configurations, the workloads may migrate across available CPU cores. This behavior is a natural artifact of how Windows schedules work across available CPU resources. However, on systems that have processor performance states that run with the adaptive processor throttling policy, this thread migration may cause the Windows kernel power manager to incorrectly calculate the optimal target performance state for the processor. This behavior occurs because an individual processor core, logical or physical, may appear to be less busy than the whole processor package actually is. On performance benchmarks that use single-threaded workloads, you may see this artifact in decreased performance results or in a high degree of variance between successive runs of identical benchmark tests.

This hotfix includes changes to the kernel power manager to track CPU use across the processor package. These changes enable visibility into the true activity level of a CPU complex and therefore help correctly calculate an increased target performance state.

Note This solution favors performance gains over power savings. Although benchmark performance scores may improve, battery life could be negatively affected. Accordingly, this kernel policy change may be disabled by a registry key to allow for maximum flexibility.
How to disable the new performance state policy behavior
Warning Serious problems might occur if you modify the registry incorrectly by using Registry Editor or by using another method. These problems might require that you reinstall your operating system. Microsoft cannot guarantee that these problems can be solved. Modify the registry at your own risk.

After you install the hotfix that is described in this article, you may use registry settings to disable the new performance state policy behavior. To do this, follow these steps:
1. Click Start, click Run, type regedit, and then click OK.
2. Right-click HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Contro l\Session Manager, point to New, and then click Key.
3. Type Throttle for the new key name.
4. Right-click Throttle, point to New, and then click DWORD Value.
5. Type PerfEnablePackageIdle for the value name.
6. Right-click PerfEnablePackageIdle, and then click Modify.
7. In the Value data box, type 0. Make sure that Hexadecimal is selected in the Edit DWORD Value dialog box, and then click OK.

Note You can type 1 in the Value data box to enable the new performance state policy behavior.
8. Quit Registry Editor.