Performance of 32-bit PAE vs. 64-bit kernel regarding 16-bit instruction

Performance of 32-bit PAE vs. 64-bit kernel regarding 16-bit instruction

[Andreas Bollhalder]

Hello

Does anyone have some advises regarding running a 16-bit executable in a
virtualized 32-bit OS under KVM ? Would it be better to run a 32-bit linux
kernel with PAE or a 64-bit kernel on the host ?

I imagine that KVM has to emulate all 16-bit instruction of a VM if
running under a 64-bit host kernel. If using a 32-bit kernel, KVM could be
able to use the vm86 mode for 16-bit instructions.

I know that PAE should be obsolete. But in my special case, I would use a
host with 16 GB of RAM running different 32-bit VMs executing 16-bit
binaries.

Thanks for your inputs.

Andreas

Re: Performance of 32-bit PAE vs. 64-bit kernel regarding 16-bit instruction

[Avi Kivity]

On 04/04/2011 04:40 PM, Andreas Bollhalder wrote:
> Hello
>
> Does anyone have some advises regarding running a 16-bit executable in a
> virtualized 32-bit OS under KVM ? Would it be better to run a 32-bit linux
> kernel with PAE or a 64-bit kernel on the host ?

It doesn't matter.  64-bit is slightly preferable.

> I imagine that KVM has to emulate all 16-bit instruction of a VM if
> running under a 64-bit host kernel. If using a 32-bit kernel, KVM could be
> able to use the vm86 mode for 16-bit instructions.

No, in both cases kvm uses whatever mode the guest asks for.

> I know that PAE should be obsolete. But in my special case, I would use a
> host with 16 GB of RAM running different 32-bit VMs executing 16-bit
> binaries.
>

With 16GB of RAM 64-bit is the way to go.

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