Re: [Qemu-devel] Testing migration under stress

[David Gibson <david@gibson.dropbear.id.au>]

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 :/.

-- 
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