[lttng-dev] Problem with adding vpid and vtid context to UST

[Mathieu Desnoyers]

* Amit Margalit (AMITM at il.ibm.com) wrote:
> So, what you're saying is that with per-UID buffers, I cannot add 
> vpid/vtid to the context because these are somehow written once per set of 
> buffers, and the buffers are shared between all applications?

No. All I said is that a channel applies to all applications.

You can add vpid/vpid/procname contexts to those channels.

Thanks,

Mathieu

> 
> If that is so - why is it that I can add 'procname' to the context and see 
> multiple processes in the trace files without any issue?
> 
> I believe I misunderstood your meaning, then. Could you please explain in 
> some more detail?
> 
> Thanks in advance,
> 
> Amit Margalit
> IBM XIV - Storage Reinvented
> XIV-NAS Development Team
> Tel. 03-689-7774
> Fax. 03-689-7230
> 
> 
> 
> From:   Mathieu Desnoyers <mathieu.desnoyers at efficios.com>
> To:     Amit Margalit/Israel/IBM at IBMIL
> Cc:     David Goulet <dgoulet at efficios.com>, lttng-dev at lists.lttng.org
> Date:   06/26/2013 09:36 PM
> Subject:        Re: [lttng-dev] Problem with adding vpid and vtid context 
> to UST
> 
> 
> 
> * Amit Margalit (AMITM at il.ibm.com) wrote:
> > Thanks for the explanation.
> > 
> > The reason I am running enable-channel is to add arguments like number 
> of 
> > subbuffers, and to select per-uid buffers. The vtid / vpid context is 
> > something I'd like to have on every channel, and I really only want a 
> > single channel...
> > 
> > In fact, it is unclear to me how to tell an application which channel to 
> 
> > use - is it even possible?
> 
> No. Currently, channels apply to all registered applications.
> 
> However, with per-PID channels, you have one set of buffers per process.
> 
> With per-UID channels, you have one set of buffers per user ID, shared
> amongst processes.
> 
> Thanks,
> 
> Mathieu
> 
> > 
> > Thanks,
> > 
> > P.S. I intend to send a man-page patch for the domain separation as you 
> > suggested.
> > 
> > 
> > Amit Margalit
> > IBM XIV - Storage Reinvented
> > XIV-NAS Development Team
> > Tel. 03-689-7774
> > Fax. 03-689-7230
> > 
> > 
> > 
> > From:   David Goulet <dgoulet at efficios.com>
> > To:     Amit Margalit/Israel/IBM at IBMIL
> > Cc:     lttng-dev at lists.lttng.org
> > Date:   06/17/2013 11:01 PM
> > Subject:        Re: [lttng-dev] Problem with adding vpid and vtid 
> context 
> > to UST
> > 
> > 
> > 
> > Hi Amit,
> > 
> > Amit Margalit:
> > > Hi,
> > > 
> > > Every time I try this, I get the following error:
> > > 
> > > Error: Error starting tracing for app pid: 5663 (ret: -1027)
> > > 
> > > Here's my sequence:
> > > 
> > > lttng create foo -o /store/
> > > lttng enable-channel -u
> > > lttng add-context -u -t vpid -t vtid -t procname
> > > lttng enable-event -u -a
> > > lttng start foo
> > > 
> > > At this point I start my application and get that error. When the 
> > application
> > > exits, I stop the tracing, and run lttng view.
> > > 
> > > The trace session seems to have worked just fine, and "procname" was 
> > indeed
> > > added to the context, but vtid and vpid were not.
> > 
> > What's going on here is that you enable a channel then add contexts. 
> This 
> > is
> > perfectly OK (although your example is missing a channel name). So, the
> > following "lttng enable-event" creates a default channel "channel0" 
> since 
> > no
> > "-c" was specified.
> > 
> > So basically, the contexts are available on the first channel and not 
> the 
> > second
> > one.
> > 
> > This sequence should work:
> > 
> > lttng create foo -o /store/
> > lttng enable-event -u -a
> > lttng add-context -u -t vpid -t vtid -t procname
> > lttng start foo
> > 
> > We should detail that a bit better in the documentation that an 
> > add-context
> > needs to be done *after* a channel is enabled. This allows you to create
> > multiple channel with different contexts.
> > 
> > Now, an other issue here in terms of usability is that the enable-event 
> > *after*
> > an enable-channel should be apply to this channel. I think there is been 
> a
> > discussion at some point on lttng-dev on in the bug tracker.
> > 
> > > 
> > > And BTW, the documentation doesn't clearly state that pid and tid are
> > > kernel-only contexts, and that one should use vtid and vpid.
> > 
> > Yes! The list of contexts accepted per domain would be quite useful and 
> I 
> > do
> > agree with you that it's missing in the doc.
> > 
> > We would be *happy* to welcome a contribution for that :).
> > 
> > Cheers!
> > David
> > 
> > > 
> > > Any help is appreciated.
> > > 
> > > Thanks,
> > > 
> > > Amit Margalit
> > > IBM XIV - /Storage Reinvented/
> > > XIV-NAS Development Team
> > > Tel. 03-689-7774
> > > Fax. 03-689-7230
> > > 
> > > 
> > > This body part will be downloaded on demand.
> > 
> > 
> 
> > _______________________________________________
> > lttng-dev mailing list
> > lttng-dev at lists.lttng.org
> > http://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev
> 
> 
> -- 
> Mathieu Desnoyers
> EfficiOS Inc.
> http://www.efficios.com
> 
> 

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com