Re: [PATCH 2/3] qemu-x86: Add tsc_freq option to -cpu

Avi Kivity
2011-07-19T15:55:37Z

On 07/19/2011 05:14 PM, Joerg Roedel wrote:
> On Tue, Jul 19, 2011 at 04:55:53PM +0300, Avi Kivity wrote:
> > On 07/19/2011 04:54 PM, Avi Kivity wrote:
> >> On 07/19/2011 04:30 PM, Joerg Roedel wrote:
>
> >>> Hmm, I planned to do the VMSTATE thing in a follow-on patch-set. The
> >>> plan is to read the VCPU tsc_freq at guest start time on !tsc-scale
> >>> hosts and migrate it over so that the destination host can set the
> >>> tsc-freq if it supports tsc-scaling.
> >>
> >> This can be done by a management tool if desired.
> >>
> >
> > Although, if we do this unconditionally (that is, also for tsc-scale
> > hosts) then we get stable tsc even without supplying a tsc frequency
> > argument... need to think about this.
>
> It has the advantage that it "just works", without the need to extend
> management tools and the like. And it makes migration more transparent
> to the guests.
>

Yes, exactly. The flip side is that automagic stuff is sometimes
unexpected and leads to breakage. I'm not sure what the right thing is.

--
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