Re: LTTng-UST vs SystemTap userspace tracing benchmarks

[Mathieu Desnoyers <mathieu dot desnoyers at efficios dot com>]

* Frank Ch. Eigler (fche@redhat.com) wrote:
> 
> Hi -
> 
> 
> mathieu.desnoyers wrote:
> 
> > [...]
> >> This is not that surprising, considering how the two tools work.  UST
> >> does its work in userspace,
> > This first part of the statement is true,
> >
> >> and is therefore focused on an individual process's activities.
> > This is incorrect. LTTng and UST gather traces from multiple processes and from
> > the kernel, and merge them in post-processing. [...]
> 
> Isn't such after-the-fact merging out of scope of the present
> microbenchmark, and in any case applicable to both tools?

This merging is indeed out of the scope of the microbenchmark, but your
statement that UST focuses on an "individual process's activities" is still
incorrect -- both SystemTAP and UST target system-wide analysis as one of their
main use-cases. We just use different techniques to get there (in-kernel probe
execution called from the instrumentation site vs streaming data through
buffers). SystemTAP allows flexibility with a powerful scripting language, which
complements the "data gathering" approach taken by UST nicely. We could even
think of combining the two approaches eventually: running scripts on information
extracted from UST buffers.

Thanks,

Mathieu

-- 
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com