condition probe argument construction in static probes

[Thomas Maier-Komor]

Hi,

is it somehow possible to conditionally enable a section of code that is responsible for constructing a probe argument.

I.e. if the first probe argument is a string, can I attach a function to the probe that will yield that string so that it doesn't have to be constructed if the probe doesn't fire?

Defining the following probe yields assembly that executes the call to expensive_argument_construction unconditionally...

DTRACE_PROBE1(myprovider,myprobe,expensive_argument_construction());

- Thomas

[Chad Mynhier]

I think you're looking for is-enabled probes. See
http://blogs.sun.com/ahl/entry/user_land_tracing_gets_better or the
current DTrace documentation.

Chad

On Fri, Jul 16, 2010 at 10:39 AM, Thomas Maier-Komor

Post by Thomas Maier-Komor
Hi,
is it somehow possible to conditionally enable a section of code that is responsible for constructing a probe argument.
I.e. if the first probe argument is a string, can I attach a function to the probe that will yield that string so that it doesn't have to be constructed if the probe doesn't fire?
Defining the following probe yields assembly that executes the call to expensive_argument_construction unconditionally...
DTRACE_PROBE1(myprovider,myprobe,expensive_argument_construction());
- Thomas
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[Thomas Maier-Komor]

yes, that is what I was looking for and what I found myself before reading your e-mail. Your answer just came unexpectedly quick.

Thanks anyway!

Cheers,
Thomas

[Thomas Maier-Komor]

replying to myself...

dtrace -h and <provider>_<probe>_ENABLED() seems to be the clue

This still yields a clear register -> nops -> jump-conditionally assembler sequence. But this is almost zero overhead...

Or is there anything better?

- Thomas