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

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Message-ID: <20100210101703.GB5035@nowhere>
Date:	Wed, 10 Feb 2010 11:17:07 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>
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 Sun, Feb 07, 2010 at 10:45:55AM +0100, Peter Zijlstra wrote:
> On Sat, 2010-02-06 at 17:10 +0100, Frederic Weisbecker wrote:
> > 
> > > > 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 :-)
> > 
> > 
> > Well, the lock hierarchy should probably be retrieved from the traces,
> > using state machines.
> > Otherwise we would need yet other lock events for that, which is going
> > to add even more overhead.
> 
> 
> Right, well you could look at adding a mode that also strips out the
> held_lock tracing, but since you really need the register class stuff to
> re-generate the class mapping, avoiding the held_lock tracing doesn't
> look like it's going to save you much, its all thread local storage.


But if we draw a tree based representation (per-instances or per-class)
from perf lock, we'll already need to get the locking scenarios from
post processing, which induce the dependencies.

I don't think it will help much.

Thanks.

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