Subject: Re: [PATCH 10/11] tracing/perf: Fix lock events recursions in the
 fast path
From: Peter Zijlstra <peterz@infradead.org>
To: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>, Lai Jiangshan <laijs@cn.fujitsu.com>,
       paulmck@linux.vnet.ibm.com, LKML <linux-kernel@vger.kernel.org>,
       Arnaldo Carvalho de Melo <acme@redhat.com>,
       Steven Rostedt <rostedt@goodmis.org>, Paul Mackerras <paulus@samba.org>,
       Hitoshi Mitake <mitake@dcl.info.waseda.ac.jp>,
       Li Zefan <lizf@cn.fujitsu.com>, Masami Hiramatsu <mhiramat@redhat.com>,
       Jens Axboe <jens.axboe@oracle.com>
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Date: Sun, 07 Feb 2010 10:45:55 +0100
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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.

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