[lttng-dev] Cross-domain influence on overhead

[Mathieu Desnoyers]

* Oestman, Fredrik (Fredrik_Oestman at mentor.com) wrote:
> Hi,
> 
> I've noticed the following somewhat puzzling effect on both Intel and
> ARM architecture computers:
> 
> If all trace events are enabled in one domain only, either kernel or
> user space, and there are lots of static tracepoints instrumented in
> the other, then these inactive tracepoints start causing overhead of
> about the same magnitude as if they were active, as if trace events
> were enabled in this domain.
> 
> Is there any obvious explanation to this behaviour?

No, this would be really surprising.

Can you provide your test script, and more details about the way you
perform your benchmarks ? How is the overhead calculated ? From how many
tracepoints hit ? How many processes spawned/exec() done ? How many
tracepoints hit per process ?

Thanks,

Mathieu

> 
> Cheers,
> 
> Fredrik Östman
> 
> http://go.mentor.com/sourceryanalyzer/
> 
> 
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-- 
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com