On Tue, 14 Feb 2006, Bob Lechner wrote:
Subject: Re: DTrace - SW tracing from app into OS kernel - Solaris---FreeBSD;  FYInfo
RJLRef: $PH/06s524/DTrace4OSDebugging.060214.txt

Scot - this is a good article, related to SWF Ch. 8,
section on trace-bassed semantics (pp 312-318, 320,325).
(printable from link at end - I've done some reading ahead.:-)

Bob Lechner

From: ** ACM TechNews; Monday, February 13, 2006 (=acmtechnews060213)

"Hidden in Plain Sight" - Queue (02/06) Vol. 4, No. 1, P. 26; Cantrill, Bryan

A lack of software observability is responsible for lengthy and often
needless diagnosis of serious performance problems that usually have a
relatively simple root cause, according to Bryan Cantrill with Sun
Microsystems' Solaris Kernel Development Group.  Software cannot manifest
itself physically, which means modifying the software is the only way to
observe the software being executed; but such constructs can slow down the
system by their very presence.  Avoiding this scenario supports the paradox
that addressing performance problems seen in production requires
replicating the problems in either a development or test environment.
Cantrill also notes that performance problems are usually introduced at the
highest software abstraction layers, but are often first seen at and blamed
on the lowest abstraction layers.  Therefore, it stands to reason that
unintentional or unnecessary work could be eliminated by moving up the
software stack to uncover underlying performance problems instead of
focusing on their cascading symptoms in the lower stack.  Shifting the
observability infrastructure's focus from software development to
production and from programs to systems is Cantrill's solution, and it
requires the optimization of software when it ships, dynamic
instrumentation of the production system, and, above all, absolute safety
of the infrastructure.  Sun's DTrace system was designed with dynamic
production system instrumentation in mind, and it offers the flexibility of
such instrumentation without sacrificing safety by drawing a line between
the system's manner of instrumentation and the framework that consumes the
data.  "The architectural elements of DTrace--safe and heterogeneous
dynamic instrumentation, arbitrary actions and predicates, and scalable, in
situ data aggregation--allow for unprecedented observability of production
systems," Cantrill writes.
http://www.acmqueue.com/modules.php?name=Content&pa=showpage&pid=361

NOTEWORTHY: Ref to APL p.7;  Experience Section - 
pp 1 and 8-10 on print-friendly version.
 A FreeBSD version being worked on part-time - Ref. 1, p. 11