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Re: statistics with intermediate results


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


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