Re: my notes from the tracing workshop

[fche at redhat dot com (Frank Ch. Eigler)]

Andrew Cagney <cagney@redhat.com> writes:

> [...]
> Overview

Thank you!

> [...]
> The exceptions were SystemTAP and SensorPoint (Wind River) (and on the
> edge, frysk).  Both SystemTAP and SensorPoint and the same basic
> approaches.  SensorPoint did have a djprobe like mechanism working,
> and nested(?) probes (where you could specify the call chain required
> to trigger the probe - it worked by watching the functions and not by
> looking at backtraces); 

We will approximate this with the incoming optimizations for
"conditional probes".

> finally the ability to replace code on live systems.

I dunno when we try to address this aspect.


> Finaly, the big and positive thing on probes was that the kernel
> markers being accepted.  [...]
>
> This is where SystemTAP and SensorPoint stood out (I think :-).  Both
> have the ability to filter events before pushing them to the recorder.
> Using SystemTAP on the kernel markers should be a wicked combination.

Yeah, we hope so!

> [Can I assume that, when there's a marked up kernel, SystemTAP
> inserts jumps instead of traps?]

Indeed - or rather, the kernel marker API does this for us.  We become
just a client.  This was what my "integration platform for probing"
title line was all about - we can attach natively to multiple
instrumentation systems and present them in a cohesive manner.


> [...]
> "DB"
> There was a strong consensus that the "internal" format of the log
> data needed to be a fast light weight database; two vendors were using
> sqlite for instance (TPTP the eclipse tool didn't but I suspect will
> shortly).  [...]

This seems rather wacky.  If they're talking about gigabytes of trace
traffic, a little wee in-memory database is a reach.  If you need to
do declarative querying, then you need a real database with indexes
and whatnot.  If you just need a big ass array, use BerkeleyDB.  If
you just want strongly typed flat data on disk, go XML.  I wish I'd
been there - perhaps my perceptions could have been falsified.


> [...] What's the status of SystemTAP on the ARM?  [...]

I haven't run it personally, but others have (Eugene Teo for the Nokia
N800).  One difficulty appears to be finding a big enough ARM box to
self-host the kernel module build process, or else cross-compiling and
cross-running.

- FChE