Re: Evaluating SystemTap for Network Response Times

[Hien Nguyen <hien at us dot ibm dot com>]

Hi Nathan,

I think what you are trying to achieve could be done with systemtap. I 
wrote a small script to monitor the tcp traffic a while back (see URL below)
http://sourceware.org/ml/systemtap/2005-q4/msg00302.html

What type of record keeping do have in mind? I am sure that someone on 
the systemtap team want to hear it.

Thanks, Hien.


Nathan DeBardeleben wrote:

> I'm looking at using SystemTap and/or [dj/k]probes to time network 
> operations inside the kernel.  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".  Obviously 
> this may involve fragmentation of packets so we'd need some way to 
> keep track that these N fragments came from this initial operation, 
> and as they close up, we know we're not completely done until all 
> fragments are done.
>
> 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.  When it comes down to it - I want to observe a 
> system and recognize outliers ("hey, this operation took 20 times 
> longer than the rest") through statistical means.
>
> I was hoping I could get some feedback from the SystemTap 
> users/developers as to whether (1) this seems feasible, (2) SystemTap 
> seems like the appropriate tool, and (3) perhaps if anyone is aware of 
> similar projects.
>
> I will be experimenting with this in a parallel computing environment 
> and with single system image tools such as bproc and the brand new 
> XCPU.  I hope I can add some value to the SystemTap community by 
> testing it out in these environments.  If this first step goes well, I 
> will be looking at using SystemTap for monitoring parallel file 
> systems and studying potential performance bottlenecks.
>
> Thanks for your time.