Re: [Qemu-devel] Testing migration under stress

[Orit Wasserman <owasserm@redhat.com>]

On 11/05/2012 02:30 AM, David Gibson wrote:
> On Fri, Nov 02, 2012 at 02:12:25PM +0200, Orit Wasserman wrote:
>> 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.
> 
> I'm not entirely sure what you mean by that.  But I do have suspicions
> based on this and other factors that the default bandwidth it is
> limiting to is horribly, horribly low.
> 
>>> 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.
> 
> Well, I realised that was true of the matrix multiply.  For video
> encode though, the output data should be much, much smaller than the
> input, so I wouldn't expect it to be dirtying memory that fast.
> 
>> 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.
> 
> Hrm.  As something really simple and stupid, I did try migrationg an
> ls -lR /, but even that didn't converge :/.
That is strange, it should converge even with the defaults,
Any special about your storage setup ?
>