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DateThu, 10 Dec 2009 13:04:12 -0500
From"Frank Ch. Eigler" <>
SubjectRe: [PATCH 2/4] ftrace - add function_duration tracer
Hi -


> > FWIW, those who want to collect such measurements today can do so with
> > a few lines of systemtap script for each of the above.
>
> Well, i dont think stap can do workload instrumentation. It can do
> system-wide (and user local / task local) - but can it do per task
> hierarchies?

It can track the evolution of task hierarchies by listening to process
forking events, and filter other kernel/user events according to
then-current hierarchy data. One primitive implementation of this is
in the target_set.stp tapset, but it's easy to script up other
policies.


> Also, i dont think stap supports proper separation of per workload
> measurements either. I.e. can you write a script that will work properly
> even if multiple monitoring tools are running, each trying to measure
> latencies?

Sure, always has. You can run many scripts concurrently, each with its
own internal state. (Overheads accumulate, sadly & naturally.)


> Also, i personally find built-in kernel functionality more trustable
> than dynamically built stap kernel modules that get inserted.

I understand. In the absence of a suitable bytecode engine in the
kernel, this was the only practical way to do everything we needed.


- FChE


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