linux-kernel - Re: [PATCH 10/11] tracing/perf: Fix lock events recursions in the fast path

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Message-ID: <1265465867.30057.507.camel@laptop>
Date:	Sat, 06 Feb 2010 15:17:47 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Ingo Molnar <mingo@...e.hu>, Lai Jiangshan <laijs@...fujitsu.com>,
	paulmck@...ux.vnet.ibm.com, LKML <linux-kernel@...r.kernel.org>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Paul Mackerras <paulus@...ba.org>,
	Hitoshi Mitake <mitake@....info.waseda.ac.jp>,
	Li Zefan <lizf@...fujitsu.com>,
	Masami Hiramatsu <mhiramat@...hat.com>,
	Jens Axboe <jens.axboe@...cle.com>
Subject: Re: [PATCH 10/11] tracing/perf: Fix lock events recursions in the
 fast path

On Sat, 2010-02-06 at 12:40 +0100, Frederic Weisbecker wrote:
> On Sat, Feb 06, 2010 at 12:24:02PM +0100, Peter Zijlstra wrote:
> > On Sat, 2010-02-06 at 12:12 +0100, Frederic Weisbecker wrote:
> > 
> > > That said, I think this is good for a first step, but we can't continue
> > > to force the lock events -> lockdep dependency in the long term. We
> > > can't have a serious lock profiling if we are doomed to suffer the
> > > slowness due to lockdep checks at the same time.
> > > 
> > > Sure we can continue to support having both, but I think we should also
> > > think about a solution to handle lock events without it in the future.
> > > That will require some minimal lockdep functionalities (keeping the
> > > lockdep map, and class hashes).
> > 
> > You mean like building without CONFIG_PROVE_LOCKING, or boot with
> > lockdep.prove_locking=0, or use echo 0
> > > /sys/modules/lockdep/prove_locking ?
> > 
> > That keeps the lock tracking but does away with all the dependency
> > analysis and was created for just such an use case as you are looking
> > at, namely lockstat.
> 
> 
> Looks pretty what I'm looking for. Except that it still continues
> to fill and keep track of the locks held by the current thread,
> namely the copies in curr->held_locks.

Which is exactly what you need for that lock hierarchy recording you
wanted :-)

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