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Re: my notes from the tracing workshop
- From: fche at redhat dot com (Frank Ch. Eigler)
- To: Andrew Cagney <cagney at redhat dot com>
- Cc: systemtap at sourceware dot org, frysk <frysk at sourceware dot org>
- Date: Fri, 01 Feb 2008 14:42:47 -0500
- Subject: Re: my notes from the tracing workshop
- References: <47A34AA2.5070404__28393.9727153212$1201883893$gmane$org@redhat.com>
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