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? 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.
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