Re: [Qemu-devel] top(1) utility implementation in QEMU

["Daniel P. Berrange" <berrange@redhat.com>]

On Tue, Oct 11, 2016 at 08:51:01PM +0800, Fam Zheng wrote:
> On Tue, 10/04 09:42, Markus Armbruster wrote:
> > >> What's the advantage over simply using another QMP monitor?  Naturally,
> > >> injecting arbitrary QMP commands behind libvirt's back isn't going to
> > >> end well, but "don't do that then".  Information queries and listening
> > >> to events should be safe.
> > >
> > > In order to avoid a Libvirt "tainted" state at production env, of course
> > > assuming qemu-top is useful there at all.
> > 
> > Adding another QMP-like protocol seems like a rather steep price just
> > for avoiding "tainted".
> > 
> > Any chance we can provide this feature together with libvirt instead of
> > behind its back?
> 
> That would be the best, but I am not sure how to make an appropriate interface.

IMHO the QMP monitor just isn't a good fit for performance monitoring due to
its inherant inefficiency wrt serialization/deserialiation. This is already
a problem with the limitation usage libvirt makes of QMP when we're collecting
data from a number of guests. I also think it is a bad choice for exposing
adhoc debugging facilities too - dynamic instrumentation is far more
flexible as it avoids us having to maintain long term stable QMP schemas
for instrumenting internal, ever changing data structures.


Regards,
Daniel
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