Re: [Xen-devel] HVM Migration of domU on Qemu-upstream DM causes stuck system clock with ACPI

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Fri, 2013-05-31 at 12:49 +0100, George Dunlap wrote:
> The problem appears to be that Linux thinks it's asking for something in 
> the future, but is actually asking for something in the past.  It must 
> look at its watch just before the final domain pause, and then asks for 
> the time just after the migration resumes on the other side.  So it 
> doesn't realize that 10ms (or something) has already passed, and that 
> it's actually asking for a timer in the past.

I suppose the root cause of this is that the type of migration being
used is completely transparent to the guest? Unlike, say, a PV aware
migration or an S3 suspend where the guest is aware and will quiesce
things such that it won't look at the time before and use it after.

TBH I don't know how you either determine or control which type of
migration is done...

>   The Xen timer driver in 
> Linux specifically asks Xen for times set in the past to return an 
> error.  Xen is returning an error because the time is in the past, Linux 
> thinks it's getting an error because the time is too close in the future 
> and tries asking a little further away.
> 
> Unfortunately I think this is something which needs to be fixed on the 
> Linux side; I don't really see how we can work around it in Xen.
> 
>   -George



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