[SeaBIOS] [PATCH] tsc: use kvmclock for calibration
Marcelo Tosatti
mtosatti at redhat.com
Thu Aug 9 21:02:03 CEST 2012
On Thu, Aug 09, 2012 at 05:20:11PM +0300, Avi Kivity wrote:
> On 08/09/2012 05:18 PM, Gerd Hoffmann wrote:
> > Hi,
> >
> >>> So what do you suggest? The options I see are:
> >>>
> >>> (1) Use this patch (with alignment issue fixed of course).
> >>> (2) Do a full kvmclock implementation. Feels a bit like overkill.
> >>> (3) SeaBIOS can fallback to the PIT for timing on machines which
> >>> have no TSC. We could do that too in case we detect kvm ...
> >>
> >> What sort of timeouts are these? If seconds, maybe the rtc would be best.
> >
> > All sorts of timeouts, from a few miliseconds to seconds.
> >
> > The problematic ones are the longer timeouts, which wait for I/O stuff
> > like disk reads complete. The stuff with smaller timeouts (like waiting
> > for AHCI link become ready) tend to finish instantly in kvm.
>
> That's not guaranteed. The AHCI adapter might be real hardware. Or the
> emulation may change.
>
> What's wrong with having a full kvmclock implementation? Instead of
> issuing rdtsc call a function pointer.
Its not necessary (someone is going to maintain the kvmclock frequency
retrieve, which patch is already here, versus maintainance of
full kvmclock).
Frequency scaling (or the software equivalent: TSC trapping) are
required for other reasons anyway.
More information about the SeaBIOS
mailing list