RE: [Xen-devel] [PATCH] Fix hvm time issue.

["Ian Pratt" <m+Ian.Pratt@xxxxxxxxxxxx>]

> >Do RTC and HPET need to be included as periodic timers? They are
never
> used
> >by Linux for ticks (it always uses PIT for jiffy updates) and I think
> >Windows is more robust against (or at least doesn't noticeably
complain
> >about) time jumps.
> >
> 
> For RTC, yes! As we know some version of Windows uses RTC as main time
> resource for timekeeping. 

I suspect that it only does this because during boot it decides that it
doesn't like the look of our pm_timer (I don't blame it!)

It would be good to invest some effort understanding why it selects RTC
-- I'm sure that it's a fall back.

Ian 


We noticed if it's not added as periodic
> timer, Windows time may go slow in SMP environment.
> In case of HPET, the answer may be no, as OS can read the
monotonically
> increased counter to see time jumps.
> 
> And as periodic timer list is per vcpu, it's also helpful to sync one
> vcpu's lapic time with its TSC, which is needed when guest calibrates
> lapic at least.
> 
> Thanks,
> Xiaowei
> 
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