linux-kernel - Re: [ltt-dev] trace a futex

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Message-ID: <20081205122822.GA25816@Krystal>
Date:	Fri, 5 Dec 2008 07:28:22 -0500
From:	Mathieu Desnoyers <compudj@...stal.dyndns.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	prasad@...ux.vnet.ibm.com, jan.kiszka@....de,
	Gian Lorenzo Meocci <glmeocci@...il.com>,
	ltt-dev@...ts.casi.polymtl.ca, linux-kernel@...r.kernel.org,
	mbligh@...gle.com
Subject: Re: [ltt-dev] trace a futex

* Peter Zijlstra (peterz@...radead.org) 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

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Mathieu Desnoyers
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