Re: [ltt-dev] trace a futex

From: Mathieu Desnoyers
Date: Fri Dec 05 2008 - 07:33:39 EST

* Peter Zijlstra (peterz@xxxxxxxxxxxxx) wrote:
> FWIW, the ftrace infrastructure has on many an occasion (even before it
> was called ftrace and specific to -rt) helped in debugging and fixing
> futex races.

Hrm, I'm not sure futex races is the key aspect of interest here.
Knowing which amount of pthread mutex lock calls ends up calling the
scheduler looks a bit more like the topic brought by this particular
use-case. Therefore, correlating the information from the nptl with the
kernel information would be useful.

Is lockdep called when a futex is taken ? Should we add instrumentation
(tracepoints) to futex.c ? If yes, was there specific instrumentation
you used with ftrace that should be added ?


Mathieu Desnoyers
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