statistics with intermediate results

[Martin Peschke]

Frank Ch. Eigler wrote:
> Martin Peschke <mp3@de.ibm.com> writes:
>>But when I use dynamic instrumentation, e.g.
>>systemtap, then I can't put some spare bytes in a
>>per request data structure to store intermediate results.
> 
> I don't understand what is blocking you.  There is no "per request
> data structure" in systemtap - spare or otherwise.

Sorry, I wasn't clear. I mean that I can't enhance kernel
data structures later on.

I could do so prior to kernel build in preparation of a tapset
that would make use of these spare bytes for temporaries, though.
I guess, this kind of access to temporaries would be fastest,
while it preserves most advantages of dynamic instrumentation.

> You can declare and use as many script-side arrays as you see fit, and
> index them as you see fit.  As long as you can recompute the same
> index tuple (a pid, request pointer address, and/or whatever) at the
> probe points that correspond to the beginning and the end of a
> computation, just use the array to store the temporaries ("start
> time").

Sounds feasible. I will give it a try. Thanks.

Martin