Re: A testing for KVM

On Thu, 2007-06-21 at 20:41 +0800, Dong, Eddie wrote:
> > I'm not sure if this affects the TSC theory or not, but note that the
> > host and guest have 250Hz PIT configured in the config.  E.g. both
> > kernels are programming the PIT to 250Hz, but guest is only
> > seeing 125Hz
> > ticks.  If I "fix" the lost interrupt to bring the ticks to a true
> > 250Hz, wall-clock time runs at 2x.  Could it still be a TSC
> > virtualization problem under these conditions? (I dont know much about
> > TSC, so I just thought I would clarify this detail)
> 
> Yes, though I am not sure if it is 2X but anyway faster in guest.
> We saw this in Xen but not that much. probably +20-30%.

Yeah, you are probably right.  I never quantified it.  I just new PIT
was 2x and clock was faster, so I assumed 2x.

> 
> From your observation, it looks like guest OS add back 100% 
> lost ticks which is quit more than I observed in Xen. Probably it
> has additional issue besides TSC. (I won't say it is a TSC
> virtualization issue, but PIT virtualization issue :-(
> Eddie


-------------------------------------------------------------------------
This SF.net email is sponsored by DB2 Express
Download DB2 Express C - the FREE version of DB2 express and take
control of your XML. No limits. Just data. Click to get it now.
http://sourceforge.net/powerbar/db2/