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Re: [Xen-devel] (XEN) HVM_PIT:missed ticks < 0

On Sun, Apr 23, 2006 at 02:39:27PM +0100, Keir Fraser wrote:
> On 23 Apr 2006, at 14:03, Ed Smith wrote:
> >After yesterday's checkins to unstable, I can no longer boot an fully 
> >virtualized guest (Intel VT).? Here is an attempt at booting a 
> >RHEL4U2-32bit uniprocessor kernel guest.? The flood of '(XEN) 
> >HVM_PIT:missed ticks < 0' messages actually occur before getting to 
> >the guest's grub menu so the guest should not matter.
> I think this has started since Edwin Zhai's PIT emulation changes. I 
> applied a further patch from him to quieten down debug output for SMP 
> guests, but if those messages are coming out that early for you then it 
> looks like maybe the patch will only hide the underlying problem.
we have an optimization in original code: pit actimer will be stopped when the 
vcpu is sched out, so we have to check the missed ticks and rearm actimer when 
each vcpu is ched in with an inactive pit actimer. 

in smp environment, if cpu 0 has checked missed ticks in pit actimer function,
then cpu 1 will probably find no missed time(now < schedule time) and complain 
when sched in. 

in summary, this redundant debug info can be safely removed. but we'll come 
perfect pit solution for smp.

>  -- Keir


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