Re: [tracecompass-dev] Question about VM tracing with LTTng and Virtual

[tracecompass developer discussions <tracecompass-dev@xxxxxxxxxxx>]

Hi,


> > Here's a presentation from almost 3 years ago on the topic, linking
> > to more recent (but still outdated) lttng-tools/ust/modules branches
> > [1]. This approach does not require trace synchronization at all.
> Ah, cool! And thanks again.
>
> Just from a really quick look, it seems similar to what the ftrace &
> trace-cmd developers are doing, in order to achieve the same.
From what I saw of ftrace virtual machine tracing (my last look at 
ftrace vm tracing was more than one year ago), iirc the guest have an 
agent that sends the events to the host, who sets the timestamp, and 
that is where they are all collected. Some students did try similar 
approaches, but the one we are proposing with the lttng branches below 
still involves taking individual traces on all guests and hosts.
> > The Trace Compass documentation was never updated to link to these,
> > as I was hoping they would make it in upstream lttng first and was
> > waiting for that. But that never happened, due to lack of interest by
> > the community.
> >
> > If you are interested, I can try to see if I can quickly rebase these
> > branches on the latest lttng 2.12, so you can try it out. You could
> > also contact the lttng community to see if they have anything in
> > their roadmap regarding this feature.
> Well, if you're up for trying a quick rebase, we are certainly up for
> giving whatever you produce a try and test it.

So I made a quick rebase, here are the branches that you can use. I 
tested very very quickly and it seems to work fine, but don't try it in 
production!

lttng-ust: 
https://github.com/tahini/lttng-ust-1/tree/statedump-notifier-2.12

lttng-tools: https://github.com/tahini/lttng-tools/tree/kvm-2.12

lttng-modules: https://github.com/tahini/lttng-modules/tree/product_uuid


On the guests, you don't necessarily need the lttng-ust and lttng-tools 
branches, unless you want to take UST traces, just lttng-modules is 
enough there, with lttng-tools 2.12.


Additionally, for those traces to work on trace compass Virtual Machine 
analysis, you need this patch on the incubator: 
https://git.eclipse.org/r/c/tracecompass.incubator/org.eclipse.tracecompass.incubator/+/122053


If you try it, please let us know how it goes!

Cheers,

Geneviève