Re: [Qemu-devel] Testing migration under stress

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

On Fri, Nov 02, 2012 at 02:07:45PM +0100, Juan Quintela wrote:
> David Gibson <david@gibson.dropbear.id.au> 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.
> >
> > 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.
> >
> > 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.
> 
> You can:
> 
> migrate_set_downtime 2s (or so)
> 
> I normally run stress, and you move the memory that it dirties until it
> converges (depends a lot of your networking).

So, I'm using tcp to localhost, so it should be really fast, but it
doesn't seem to be :/.  I suspect there are some other bugs here.

> Doing anything that is really memory intensive is basically never gonig
> to converge.

Well, I didn't think the loads I chose would be memory limited
(especially the video encode), but..

-- 
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