Re: [Qemu-devel] [PATCH 1/2] KVM: fix i8259 interrupt high to low transition logic

[Maciej W. Rozycki]

On Wed, 12 Sep 2012, Matthew Ogilvie wrote:

> Also, how big of a concern is a very rare gained or lost IRQ0
> actually?  Under normal conditions, I would expect this to at most
> cause a one time clock drift in the guest OS of a fraction of
> a second.  If that only happens when rebooting or migrating the
> guest...

 It depends on how you define "very rare".  Once per month or probably 
even per day is probably acceptable although you'll see a disruption in 
the system clock.  This is still likely unwanted if the system is used as 
a clock reference and not just wants to keep its clock right for own 
purposes.  Anything more frequent and NTP does care very much; an accurate 
system clock is important in many uses, starting from basic ones such as 
where timestamps of files exported over NFS are concerned.

 Speaking of real hw -- I don't know whether that really matters for 
emulated systems.  Thanks for looking into the 8254 PIT in details.

  Maciej