LWN: Comments on "Conditional tracepoints"

Conditional tracepoints

Auders — Wed, 08 Dec 2010 11:02:36 +0000

The condition should be reflected in the format then, so that the tool used to read the tracepoint can know about it.

Conditional tracepoints

dag- — Fri, 03 Dec 2010 10:16:16 +0000

You removed the next sentence which gives a clue.

> So, if somebody other than the initial developer wants to use the tracepoint, they could misinterpret a lack of output as a sign that the surrounding code is not being executed at all.

The people using the tracepoints are not necessarily kernel developers, and in most cases will not be tracing while at the same time looking at the source-code.

Conditional tracepoints

intgr — Thu, 02 Dec 2010 16:56:32 +0000

> There is one potential problem in that the condition is now hidden deeply
> within the definition of the tracepoint; that definition is usually found
> in a special header file far from the code where the tracepoint is
> actually inserted. At the tracepoint itself, the condition which might
> cause it not to fire is not visible in any way.

Why not use code comments? their purpose after all is to inform other coders of things that might not be obvious at first.

Conditional tracepoints

mjthayer — Thu, 02 Dec 2010 10:16:07 +0000

> "Tracing those calls could create a stream of useless events which would have to be filtered out by PowerTop, causing PowerTop itself to require more power."

It does make me wonder why the filtering logic couldn't just be in PowerTop, as having the tracepoint on is clearly not the normal case. I assume that it would have generated enough extra work and really changed the systems power usage enough to make PowerTop's analysis harder.

Conditional tracepoints

thedevil — Thu, 02 Dec 2010 03:58:45 +0000

"Tracing those calls could create a stream of useless events which would have to be filtered out by PowerTop, causing PowerTop itself to require more power."

LOL! Thanks for this bit of typical LWN humor. Sometimes I think the Editor has been born on other shores where this gift is more common :)