Re: live migration question

[Juergen Gross <juergen.gross@ts.fujitsu.com>]

On 01/30/2012 05:26 PM, Jan Beulich wrote:
>>>> On 30.01.12 at 13:24, Juergen Gross<juergen.gross@ts.fujitsu.com>  wrote:
>> To avoid this stall I tried to start a little daemon on the target machine
>> and watch for a new BS2000 domain to show up due to live migration. I wanted
>> to map the domain memory as soon as the needed mapping information located
>> in a fixed guest mfn was transferred. Discovery of the new domain works as
>> expected, but I'm not capable doing any memory mapping until the restore of
>> the domain is finished. The mapping ioctl using IOCTL_PRIVCMD_MMAP returns
>> EINVAL until xc_restore is finished (more or less).
>>
>> Why can xc_restore do the mapping while I can't? I know xc_restore is using
>> IOCTL_PRIVCMD_MMAPBATCH_V2, but I can't see a difference which should matter
>> between those two, as both are using the same hypercall to update the dom0
>> page tables.
> I cannot immediately think of a reason (and indeed the difference
> between the two is only how errors get handled), so I wonder
> whether you checked where the - pretty generic - -EINVAL is
> coming from. You also didn't mention whether any hypervisor log
> entries are associated with you failed attempts.

I'll start to add some logging to the hypervisor today.

No hypervisor logs were produced in my tests, despite of setting

debug=yes loglvl=all guest_loglvl=all

as boot parameters.

I've made an additional test using xm save/xm restore to see if the same
problem shows up. It does NOT. Mapping succeeds at once while restoring
memory is still running. I always thought xm restore and live migration on
the target machine are more or less the same. This seems not to be true.


Juergen

-- 
Juergen Gross                 Principal Developer Operating Systems
PDG ES&S SWE OS6                       Telephone: +49 (0) 89 3222 2967
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