[ltt-dev] performance results I measured with the latest lttng patches

Mathieu Desnoyers compudj at krystal.dyndns.org
Wed Sep 24 11:14:54 EDT 2008

* Michael Rubin (mrubin at google.com) wrote:
> On Wed, Sep 24, 2008 at 12:25 AM, Jan Blunck <jblunck at suse.de> wrote:
> > Isn't lttng-compile-out missing here? Or did you ran the same base kernel?

Hi Michael,

> I believe it's the same base kernel. Which means we have about a 2.3%
> performance penalty for just compiling the LTTng code in with no
> markers enabled. We love the functionality of LTTng, but that is a
> non-starter for us.  We are motivated to help make this better.

Hrm, this result surprises me.

> I am curious what the expectations and goals the lttng efforts have
> for performance in these scenarios. Do you guys have a goal for perf
> impact in the situations of not configured (or not compiled) vs
> configured (compiled in) but no trace points enabled vs tracepoints
> enabled?

yeah, about, say.. unnoticeable ? :)

> What sort of benchmarks are you using to test performance? That way we
> can use the same ones to better compare notes. Do you have access to
> HW with lots of cores?

A while ago I used a mix of lmbench and my own microbenchmarks (running
markers and tracing in tight loop in a kernel module to have an idea of
the cache-hot behavior). I've recently seen from Jiaying posts that
tbench does a very good job at stressing LTTng, given it uses system
calls extensively.

I have a dual-quad cores at my lab, I'll run some tbench tests on this
setup to try to figure out what went wrong. I guess there might be some
option enabled when it shouldn't, or maybe I made some sort of stupid
error.... :) Anyway, that should not be too hard to find, hopefully.


> Thanks in advance,
> Michael Rubin

Mathieu Desnoyers
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