Re: [Qemu-devel] Testing migration under stress

[Juan Quintela <quintela@redhat.com>]

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).

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

Later, Juan.