Re: Evaluating SystemTap for Network Response Times

[Nathan DeBardeleben <ndebard at lanl dot gov>]

Frank Ch. Eigler wrote:
> Nathan DeBardeleben <ndebard@lanl.gov> writes:
>
>  
> > [...] Specifically, we want to time the point
> > when a socket send operation leaves user space, entering kernel space,
> > down to the point where the kernel says "it's done, sent".  [...]
> >
> > Initially this looks just like the kind of thing I could do with
> > SystemTap but I worry that the scripting language will be too
> > restrictive to allow me to allocate these types of data structures
> > to do record keeping.
> >     
>
> I hope it is exactly this kind of complex instrumentation with which
> systemtap could show its prowess.  I would like to help you make it
> work.
>   
So should I take this as a volunteering of your assistance in answering 
questions? :)   We are heavily involved in dynamic application 
instrumentation (dyninst, Open|SpeedShop, apps/tools like those) but 
we're starting to see a major need to go a step deeper into looking at 
the kernel.  We're in the position to really test out SystemTap/kprobes 
on a variety of different architectures and stress loads and even (if 
necessary/accepted) to help extend and fix SystemTap.

I've read all the online documentation and written some simple test 
taps, like the examples on the web.
Before I start tracing the 2.6.x kernel for the places we want to 
instrument this network study I wondered - have you guys had already 
started a "tapset" for this issue?

The other question I had was if SystemTap intends to look into djprobes 
in the future.  I've read it mentioned in bits and pieces on your 
mailing list but haven't yet pieced together a 'big picture' of the 
SystemTap opinion and/or plans for djprobes.  From our studies, it's a 
lot lighter weight than kprobes and we're hoping to go with something 
like SystemTap so that in the future you guys might implement a way for 
users to choose which probe they want at insert time.

Take care.

-- Nathan
Correspondence
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Nathan DeBardeleben, Ph.D.
Los Alamos National Laboratory
Parallel Tools Team
High Performance Computing Environments
phone: 505-667-3428
email: ndebard@lanl.gov
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