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?
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 <[email protected]> To: Amit Margalit/Israel/IBM@IBMIL Cc: David Goulet <[email protected]>, [email protected] Date: 06/26/2013 09:36 PM Subject: Re: [lttng-dev] Problem with adding vpid and vtid context to UST * Amit Margalit ([email protected]) 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 <[email protected]> > To: Amit Margalit/Israel/IBM@IBMIL > Cc: [email protected] > 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 > [email protected] > http://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com
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