Re: CONFIG_SMP required for save/restore and migration: bug?

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

On Tue, Aug 27, 2013 at 01:09:41AM +0200, Luca Lesinigo wrote:
> Dear list, I was about to write here seeking for help because my Ubuntu domUs were migrating just fine while my Gentoo ones were just hanging "freezed" after attempting migration, or after saving and restoring on the same node.
> 
> After some more tinkering around, I nailed the issue to my kernel config which was stripped down to the bare minimum: no hardware drivers, no loadable modules... and no SMP. After enabling SMP support my domU were able to migrate without problems. The same happens on 3.2.x and on 3.10.7 kernels.
> 
> Before playing with many different kernel configurations, I searched Xen's wiki and googled around but could not find anything related to this issue.
> 
> So: with my config, non-SMP kernels will freeze after restore, while activating CONFIG_SMP and nothing else will make this problem disappear. Maybe non-SMP kernels are supposed to migrate but there's a software problem, or maybe SMP is a requirement but is not documented (or at least I wasn't able to find it). Maybe it's not CONFIG_SMP but one of its dependencies.
> 
> Either way, I'm writing to the list to report this experience, maybe it is a (software or documentation) bug?

It could also be a dependency issue. Meaning if you undef CONFIG_SMP it won't pick up the
rest of the code - say the code needed for migration.

That would be odd and buggy.

If you compare the two .config files what does CONFIG_SMP=y add extra?

Are these PVHVM or PV domUs?

Thanks!

> 
> I'll keep an eye to the list in the next days, if you need any other detail just ask.
> 
> Thank you for developing Xen, keep up with the good work!

Thank you.
> 
> --
> Luca Lesinigo
> 
> 
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