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Re: statistics with intermediate results
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