Re: The SMP RHEL 5.1 PAE guest can't boot up issue

Avi Kivity
2008-03-04T11:38:16Z

Avi Kivity wrote:
> Dong, Eddie wrote:
>>>> I don't know if the patch was still needed now, since it was posted
>>>> long ago(I don't know which issue it solved). I'd like to post a
>>>> revert patch if necessary.
>>>>
>>> I believe the patch is still necessary, since we still need to
>>> guarantee that a vcpu's tsc is monotonous. I think there are three
>>> issues to be addressed:
>>>
>>> 1. The majority of intel machines don't need the offset adjustment
>>> since they already have a constant rate tsc that is synchronized on
>>> all cpus. I think this is indicated by X86_FEATURE_CONSTANT_TSC
>>> (though I'm not 100% certain if it means that the rate is the same
>>> for all cpus, Thomas can you clarify?)
>>>
>>
>> So why not make the TSC_OFFSET adjustment conditional?
>>
>
> Yes, that's what I meant. We just need to be sure that this is what
> X86_FEATURE_CONSTANT_TSC means.

I changed tsc offset adjustment to only allow forward adjustment. Since
hosts with synced tsc never require positive adjustment, they should now
have better quality tsc.

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