[ltt-dev] UST manual

Matthew Khouzam matthew.khouzam at ericsson.com
Mon Feb 28 17:21:47 EST 2011

On 11-02-22 01:45 AM, Amir wrote:
> Hi,
> I'm really new to UST and generating user-space traces for software 
> systems.
> I followed the instruction provided at: 
> http://lttng.org/files/ust/manual/ust.html
> Packages were successfully installed and I could generate a trace 
> following the provided example for markers.
> Still I have a few questions for which I couldn’t find answers in the 
> manual.
> - what are 'event categories' and 'channels'?
A channel is as it's name indicates a way to communicate with UST. In 
the trace, each channel has N files allocated to it where N is the 
number of cores you have. Each channel also has a certain amount of 
memory allocated to to. I tend to only use the channel "UST" as it makes 
my life easier, but then again, I am a very bad person who's been caught 
doing unsavory things to programs for a long while and that says 640k 
ought to be enough for anybody without signs of irony.

Perhaps someone more knowledgeable in UST can show me the error in my ways.
> - is it possible to generate a method call trace using markers? would 
> it work just for C applications?
You mean like "
void trace_result( int n ) {
trace_mark(  ust, myevent, "%d" ,n);
}" ?
Yes, it's what I do... look into tracepoints though, you're halfway 
there with that.

> - it seems like 'Appendix x' is missing, how would it be possible to 
> have some information about the formatting
I think Appendix X was a placeholder, not sure, I didn't write it ;) .
> Thanks,
> Amir
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