Re: performance tuning, problem with paravirtualized clock

Nikola Ciprich
2008-04-06T21:57:02Z

Hi Anthony!
Anthony Liguori wrote:
> I would think you should get about 70% of native with what you've done
> about. I've not seen instabilities with CONFIG_KVM_CLOCK myself.
>
> Setting up a hugetlbfs mount and using -mem-path may give you a bit of
> a bump too but I'd be surprised if it was more than 5%
I've tried it now, and starting kvm with -mem-path pointing to hugetlbfs
mounted dir immediately fails and I see following message in dmesg of host:
VM: killing process qemu-system-x86
pointing to tmpfs mounted dir seems to work, I'll measure performance
gain...

>
> The next biggest win you're going to see is using NPT (available in
> the recent AMD Barcelona/Phenom processors). NPT + hugetblfs should
> get you pretty close to native (I'd reckon 95-98%).
Yup, it seemed to me that kvm performes WAY better on my phenom based
home desktop! I'll check that later too
>
> On the Intel side of things, you'll have to wait until the Nehalem
> which will support EPT (which is Intel's version of NPT).
>
> Can you be specific about your guest configurations? Are you using
> -smp 8?
yes, I'm using -smp 8
>
> Regards,
>
> Anthony Liguori