Re: [Xen-devel] Migration and CPU type?

[Anthony Liguori <aliguori@xxxxxxxxxx>]

Noam Taich wrote:
> I created my guest on my Athlon and tried to migrate it to my laptop 
> running a Pentium M. The guest failed.
As a general principle, migrating between AMD and Pentium chipsets is a 
bad idea.
If you google a bit, VMware has VMotion compatibility tables that match 
which processor families they consider "safe" to migrate to and from.
Regards,

Anthony Liguori
> When I tried the opposite, creating it on my laptop and migrating it 
> to my Athlon, it worked… Not only that, but now, after being forged in 
> the flamed of the Pentium M, I could migrate it BACK from the Athlon 
> to the laptop…then to an Opteron… That was fun. It can actually 
> function like a roaming guestJ
> One problem is that OSs usually gather information on the system they 
> are running, on all the features the CPU offers them.
> What if one or more of the features is not supported on the target 
> host? You think it will crash?
> NOT necessarily. It won't crash if there's currently no running code 
> on the guest that uses that feature.
> I believe It will also be a problem if some code that USES such a 
> feature is ON the guest RAM image, but for some reason is not
> Currently running, until a user dose something…this could lead to 
> seemingly unexplained crashes.
> I am also interested in future compilations/executions on the migrated OS…
>
> It can be affected too…
>
> NOW, having said that… completely preventing migration between CPUS 
> that are not 100% compatible may not be a good idea…
> after all…you may KNOW that the current configuration will work on the 
> other machine (or you may know it was migrated from there
> In the first place), and you may need to do a hardware upgrade with no 
> downtime… no reason to prevent this…
> I discovered that as long as you create the guest on the machine with 
> the LEAST amount of features among the ones it may
> Be migrated to (the one that has NO feature the other ones don't have) 
> , the migration seems to work fine in every direction.
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