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Date: Sat, 30 Jan 2010 19:57:37 +0100
From: Frederic Weisbecker <fweisbec@gmail.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Hitoshi Mitake <mitake@dcl.info.waseda.ac.jp>, Ingo Molnar <mingo@elte.hu>,
       Paul Mackerras <paulus@samba.org>,
       Arnaldo Carvalho de Melo <acme@redhat.com>,
       Thomas Gleixner <tglx@linutronix.de>,
       "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
       LKML <linux-kernel@vger.kernel.org>
Subject: Re: Lock dependency based tree report in perf lock
Message-ID: <20100130185736.GC5675@nowhere>
References: <20100129231723.GB5052@nowhere> <1264841188.24455.54.camel@laptop>
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On Sat, Jan 30, 2010 at 09:46:28AM +0100, Peter Zijlstra wrote:
> On Sat, 2010-01-30 at 00:17 +0100, Frederic Weisbecker wrote:
> > 
> > 
> > Anyway, that's just an idea, not trivial I must admit.
> 
> lockdep actually collects all this information, so writing it out isn't
> too hard.



Lockdep collects the theorical dependencies but not the practical
scenarios.

Say B and C depend on A, you'll get:

   A
  / \
 B   C

But nothing can tell you that if A is taken, B and C will always
be taken. You may have different scenarios based on this dependency,
which is not something that lockdep logs, right?