On Tue, Jan 04, 2011 at 05:28:02PM +0000, Gianni Tedesco wrote:
> On Tue, 2011-01-04 at 17:09 +0000, Ian Campbell wrote:
> > Which ever one of you started it: Please don't top post.
> >
> > > On Sat, Oct 09, 2010 at 10:15:20AM +0800, wei song wrote:
> > > > added timer_mode =2 and tsc_mode = 1 and viridian=1 into your
> > > > configure
> > > > file.
> >
> > On Mon, 2010-10-11 at 11:10 +0100, Mark Adams wrote:
> > > I can try this, but can you please confirm what these options do?
> >
> > viridian=1 turns off support for the Hyper-V virtualisation
> ^^^ on ;)
>
> > compatibility layer. Not many of these are actually supported but AFAIK
> > one or two are and can affect the behaviour of Win2008 (although you
> > would hope it was for the better!)
> >
> > According to xmexample.hvm: tsc_mode : TSC mode (0=default, 1=native
> > TSC, 2=never emulate, 3=pvrdtscp).
>
> >From xen/include/asm-x86/time.h:
> /*
> * PV TSC emulation modes:
> * 0 = guest rdtsc/p executed natively when monotonicity can be guaranteed
> * and emulated otherwise (with frequency scaled if necessary)
> * 1 = guest rdtsc/p always emulated at 1GHz (kernel and user)
> * 2 = guest rdtsc always executed natively (no monotonicity/frequency
> * guarantees); guest rdtscp emulated at native frequency if
> * unsupported by h/w, else executed natively
> * 3 = same as 2, except xen manages TSC_AUX register so guest can
> * determine when a restore/migration has occurred and assumes
> * guest obtains/uses pvclock-like mechanism to adjust for
> * monotonicity and frequency changes
> */
>
> >
> > Timer mode is apparently "0=delay virtual time when ticks are missed;
> > 1=virtual time is always wallclock time".
>
> It's all explained in xen/include/public/hvm/params.h
>
> AIUI, timer_mode=0 means if timer ticks were missed then they all get
> re-injected in to the guest when next run. IOW if 5 ticks were missed
> you get 5 IRQ's in succession and the clock time is incremented stepwise
> with them. I think it should never be used unless the OS simply counts
> ticks to figure out the time (which they don't).
>
> 1 is default and means the same except virtual time is always up to date
> when re-injecting missed ticks.
>
> 3 i'm not sure about but sounds like some variant of 4?
>
> 4 is where missed ticks delivered in one 'late tick'
>
> Gianni
>
>
All, Thanks for input. Do you agree that the -best- setting to maintain
stable time for 2008 R2 hvm guests is to use timer_mode = 2, tsc_mode =
1 and viridian = 1 ?
Best Regards,
Mark
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