static probes [LWN.net]

static probes

Posted Aug 7, 2007 22:15 UTC (Tue) by fuhchee (subscriber, #40059)
In reply to: static probes by bcantrill
Parent article: On DTrace envy

> That's a pretty gutsy assertion

And a correct one, as we seem to be in vigorous agreement. Many scripts
use the static probes, especially the ones one might use to start analyzing
a problem. There is nothing wrong with "depending" on static probes in this
sense, so I don't see why you would object.

> from someone who, to the best of my knowledge, has never used DTrace.

The best of your knowledge needs to get better.

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Vigorous disagreement

Posted Aug 7, 2007 22:34 UTC (Tue) by bcantrill (guest, #31087) [Link]

Frank, you write:

That's a pretty gutsy assertion
And a correct one, as we seem to be in vigorous agreement.

No, no we're not -- not at all. You wrote this:

...but almost all of the interesting data that is gathered comes from providers other than fbt, and these are implemented with static probes.

That is wrong, and I am not in agreement with it whatsoever. It's wrong in two dimensions. The first being that "all...interesting data comes from providers other than fbt"; as I said (clearly, I thought) fbt and pid often are used as an investigation proceeds from the symptoms of a suboptimal system to the root-causes of that suboptimality in the implementation. So it's a gross mischaracterization to dismiss their role in DTrace. The second way in which your statement is incorrect is the implication that "providers other than fbt ... are implemented with static probes." This shows complete ignorance of the pid provider, which can instrument any instruction in any running process, and is the workhorse of user-level instrumentation.

You also write:

from someone who, to the best of my knowledge, has never used DTrace.
The best of your knowledge needs to get better.

Fair enough; allow me to rephrase: "someone who, if they have used DTrace at all, appears to have learned nothing from the experience." Better?

Please don't misquote

Posted Aug 12, 2007 18:49 UTC (Sun) by felixfix (subscriber, #242) [Link]

Your credibility in this argument just took a big dive. fuhchee said "almost all of the interesting data" and you left out the "almost", which changes the meaning considerably. Besides which, you yourself say "much investigation does indeed start with probes from SDT- and USDT-provided probes -- but it often finishes with probes from fbt and pid" which certainly implies that a majority of investigations begin with SDT and USDT, which also implies that SDT and USDT are "more" used than anything else. Maybe "almost all" is an exageration of "most", but leaving out the "almost" is a misquote twisting his words to match your thoughts.