Re: [RFT] kvm with Windows optimization

Avi Kivity
2007-10-25T18:34:13Z

Anthony Liguori wrote:
> Avi Kivity wrote:
>
>> This is a request for testing of an experimental kvm feature that
>> dramatically accelerates some Windows releases (when running with the
>> ACPI HAL, and especially with guest SMP). The feature detects accesses
>> by the guest to the Task Priority Register (TPR) and patches them at
>> runtime to a kvm-friendly code snipped that is provided by the BIOS.
>>
>> The upshot of all that is that
>> http://kvm.qumranet.com/kvmwiki/Windows_ACPI_Workaround is no longer
>> required, and Windows SMP no longer runs like a dog; it's quite snappy
>> from my very limited testing.
>>
>> Please download the test release from
>> http://people.qumranet.com/avi/tpr-opt-1.tar.gz and give it a spin.
>> Once it has received some exposure, I'll merge it into mainline.
>>
>> Credit for the original idea is due to Ben Serebrin.
>>
>>
>
> BTW, is it wise to enable this by default for all guests? Ignoring the
> fact that we're modifying guest's memory without its knowledge, if a
> guest unmaps the VA mappings for the BIOS then all sorts of problems
> could occur

I'd like to make this the default and add an option to disable it.

The code is careful to try to detect Windows, and we can tighten the
check in case it misfires. I'd like things to Just Work (they may also
Just Crash, but hopefully we can fix this).

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