statistics with intermediate results

[Jose R. Santos]

Martin Peschke wrote:

>I guess, one could report all events, like send time, receive
>time and so on, through systemtap and defer all processing to
>a user land script. That's the Linux Kernel Event Trace Tool
>approach:
>http://sourceware.org/ml/systemtap/2005-q4/msg00458.html
>
> From a performance point of view, I am not sure it is the
>fastet way of getting latencies, because it involves huge
>amounts of data being generated by probes and being
>reported through relayfs, while we can't use the benefits
>of immediate data reduction as provided systemtap's statistics.
>

One of the things that we are doing with the Kernel event trace tool is 
add the capabilities for users to add their own trace hooks.  One can 
chose to probe a single point in the kernel instead of doing a full 
trace.  In the end though it really depends on which has the greater 
overhead; doing aggregation in the systemtap script or printing every 
single event to userspace.  It's obvious who win here.

One key advantage of having a trace is that it allows you to run once 
and analyze in many different ways.  Like you said, histograms can be 
very useful.

Good Luck

-JRS