Re: qemu-kvm upstreaming: Do we need -no-kvm-pit and -no-kvm-pit-reinjection semantics?

[Marcelo Tosatti <mtosatti@redhat.com>]

On Thu, Jan 19, 2012 at 09:33:51AM +0100, Jan Kiszka wrote:
> Hi all,
> 
> I've finished a first version of cleaned-up in-kernel KVM PIT support.
> That will be rolled out once the base support for irqchip has been merged.
> 
> I'm now wondering if and how to model two control knobs we have in qemu-kvm:
> 
>  o -no-kvm-pit, ie. disable the in-kernel PIT even when {A,IOA,}PIC
>    are kernel based (default: off, ie. use in-kernel PIT)

It can be useful for debugging.

>  o -no-kvm-pit-reinjection, ie. control over the lost ticks reinjection
>    logic in the kernel (default: off, ie. do reinject)

If the guest kernel does not compensate for lost ticks, reinjection is 
needed. Otherwise, it might cause problems.

Therefore this option is needed.

> So far I dropped the former and modeled the latter via a qdev property.
> But I tend to think that even the latter knob is superfluous. In that
> case I would also deprecate the original switches in qemu-kvm, just like
> recently done with -tdf.
> 
> Other thoughts?
> 
> Jan
> 
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> Siemens AG, Corporate Technology, CT T DE IT 1
> Corporate Competence Center Embedded Linux
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