[ltt-dev] Dobut: Why LLtrace?

[Pierre-Marc Fournier]

VISHAL KANAUJIA wrote:
> Hi,
>   I am newbie to world of LLTrace. I read a couple of papers and as per
> my understanding LLtrace is kind of kernel instrumentation that would
> facilitate application performance data. What I could not comprehend was
> that how could LLTrace data better, more detailed than simple
> statistical sampling. Besides considering the inroduction of advanced
> PMUs in processors how would LLtrace helps uniquely and more efficiently?
> 
> Please bear with me if I sound stupid.
> 
> Thanks,
> Vishal
> 

I assume you talk about LTTng here.

Some performance problems are simply too high-level to be understood
with only statical approaches. Have a look at the paper "Linux Kernel
Debugging on Google-sized clusters".
http://ltt.polymtl.ca/papers/bligh-Reprint.pdf
You will find in it many examples of problems where statistical
approaches would not have worked very well.

pmf