[ltt-dev] tracepoint layer and marker layer

[Jan Blunck]

On Wed, Sep 17, Jiaying Zhang wrote:

> Hi Folks,
> 
> I have a general question about LTTng kernel code. As I understand, LTTng
> adds an extra tracepoint layer between the traced subsystems and the
> marker layer. The extra code added by the tracepoint layer seems to
> introduce
> noticeable overhead according to my measurements. I wonder whether it will
> be more efficient and simpler if we let subsystems call the marker layer
> directly?

I guess that was how it worked before the tracepoints. Although I don't
fully understand why the redirection is necessary.

> Any thought?

You could try to disable the lttng-instrumentation-*-tracepoints-probes.patch
patches. These patches register tracepoint probes just to setup a marker. I
guess this is where the overhead is coming from.

Anyway, do you have numbers that you can share with us? Mathieu still has the
performance numbers with the marker patches in the tracepoints.patch. I guess
he would be glad if he could update them.

Regards,
	Jan

-- 
Jan Blunck <jblunck at suse.de>