Re: performance specs on VT-x vmenter/exit

[Avi Kivity <avi-atKUWr5tajBWk0Htik3J/w@public.gmane.org>]

Dan wrote:
> Greetings Honorable KVM Devs!
>
> I am doing research on the performance characteristics of the Intel
> VMX instructions, specifically with respect to KVM. I need to count
> the cycles for a VMENTER and VMEXIT instruction under various
> conditions. (But getting it to work at all would be cool :)
>
> So the idea is to drop the cycle count in a register from the VMM,
> force a VMENTER, drop the count in a different register, and force a
> VMEXIT. Then get a last count and do appropriate adding/subtracting.
> I'm working with a 2.6.22.6 <http://2.6.22.6> vanilla kernel on an
> Core2Duo with KVM-54.
>
> Questions:
>  Is there a better way to get these numbers?
>  If not, where in the KVM source should I aim to put these
> instructions (file/line number/general area)?
>  Any tips on forcing a vmexit out of the guest immediately after the
> count?
>
> Thank you so much for your time.
>   :dan


Have a look at user/test/x86/vmexit.c, which does exactly that.

-- 
Do not meddle in the internals of kernels, for they are subtle and quick to panic.


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