Hyper-V virtual machines exhibit slow startup and shutdown

This article provides help to fix slow virtual machines (VMs) startup or shutdown performance issues.

Applies to:   Windows Server 2008 R2 Service Pack 1
Original KB number:   2532917

Symptoms

On Windows Server 2008 R2, when starting or shutting down guest VMs that use large amounts of memory (for example, 32 GB per VM) and running on a virtualization host with a large number of logical processors (for example, 64LPs), you may observe slow VM startup or shutdown performance.

Cause

This is caused by the time required for the hypervisor to send IPIs to a large number of processors, and the fact that the processors have entered a deep processor idle power state (ACPI C-state). Waking the processor to deliver the IPI takes longer than delivering an IPI to a processor that does not have to exit the deep idle sleep state. The number of IPIs that must be sent during startup and shutdown increases with the amount of memory a VM is configured to use, and an IPI must be sent to each processor in the system. Thus, using deep ACPI C-states on systems with a large number of CPUs and using VMs with large amounts of memory will compound the causes and result in noticeable VM startup and shutdown delays.

Resolution

You can disable the Advance Configuration and Power Interface (ACPI) C-states by using a BIOS firmware option on the computer. If the firmware does not include this option, a software workaround is available. You can disable the ACPI C2-state and C3-state by setting a registry key. To do this, follow these steps:

1. At a command prompt, run the following command:

   reg add HKLM\System\CurrentControlSet\Control\Processor /v Capabilities /t REG_DWORD /d 0x0007e066
   

2. Restart the system.