Re: thoughts [re LTT]

["Frank Ch. Eigler" <fche@redhat.com>]

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Hi -

On Mon, Sep 26, 2005 at 01:44:42PM -0400, Mathieu Desnoyers wrote:

> [...]  We have a kernel tracer (LTTng) and a trace viewer (LTTV)
> which are based on static kernel instrumentation.  One of the main
> advantages of the LTTng tracing code is that it is fast. It seems to
> be a downside of SystemTAP.

Static instrumentation of course allows one to avoid the breakpoint
fault of kprobes.  At some point, we too will support static
instrumentation, with our own variant and/or attaching to
LTT/LKST/etc. hooks.

> We use a code generator that takes an event description to generate
> the tracing code that can be inserted through module loading.

This is quite clever, but addresses a different clientele.  LTT-type
techniques may be sufficient iff:

 - one may patch one's kernel with the tracing infrastructure
 - the set of trace event points are all hard-coded
 - the data made available at those points are all hard-coded
 - the computation performed upon those data/events is limited to
   little besides filtering / printing

I suspect we can get the best of both worlds over time.

- FChE

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