Re: [Qemu-devel] Testing migration under stress

[Orit Wasserman <owasserm@redhat.com>]

On 11/02/2012 05:10 AM, David Gibson wrote:
> Asking for some advice on the list.
> 
> I have prorotype savevm and migration support ready for the pseries
> machine.  They seem to work under simple circumstances (idle guest).
> To test them more extensively I've been attempting to perform live
> migrations (just over tcp->localhost) which the guest is active with
> something.  In particular I've tried while using octave to do matrix
> multiply (so exercising the FP unit) and my colleague Alexey has tried
> during some video encoding.
>
As you are doing local migration one option is to setting the speed higher
than line speed , as we don't actually send the data, another is to set high downtime.

> However, in each of these cases, we've found that the migration only
> completes and the source instance only stops after the intensive
> workload has (just) completed.  What I surmise is happening is that
> the workload is touching memory pages fast enough that the ram
> migration code is never getting below the threshold to complete the
> migration until the guest is idle again.
> 
The workload you chose is really bad for live migration, as all the guest does is
dirtying his memory. I recommend looking for workload that does some networking or disk IO.
Vinod succeeded running SwingBench and SLOB benchmarks that converged ok, I don't
know if they run on pseries, but similar workload should be ok(small database/warehouse).
We found out that SpecJbb on the other hand is hard to converge.
Web workload or video streaming also do the trick.

Cheers,
Orit

> Does anyone have some ideas for testing this better: workloads that
> are less likely to trigger this behaviour, or settings to tweak in the
> migration itself to make it more likely to complete migration while
> the workload is still active.
>