linux-kernel - Re: [PATCH 1/3] lockdep: Move lock events under lockdep recursion protection

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Message-ID: <20100309234518.GE5058@nowhere>
Date:	Wed, 10 Mar 2010 00:45:20 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Jens Axboe <jens.axboe@...cle.com>
Cc:	Ingo Molnar <mingo@...e.hu>, LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.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>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	Masami Hiramatsu <mhiramat@...hat.com>
Subject: Re: [PATCH 1/3] lockdep: Move lock events under lockdep recursion
	protection

On Tue, Mar 09, 2010 at 09:34:10AM +0100, Jens Axboe wrote:
> I went to try this on 2.6.34-rc1 to see how much it would improve things
> here. With 2.6.34-rc1, a
> 
> $ time sudo perf lock record ls /dev/shm
> 
> essentially hangs the box, it ends up crashing hard (not just live
> locked like before). With the patch in place, it does eventually finish:
> 
> real    0m21.301s
> user    0m0.030s
> sys     0m21.040s
> 
> The directory is empty.


Hehe :-)

That said you are probably missing a part of the puzzle.
This patch avoids the scary recursions we had. But there
is another separate patch that fixes the buffers multiplexing
dependency we had. Buffering is now done per cpu.

You need this patch:

	commit b67577dfb45580c498bfdb1bc76c00c3b2ad6310
	Author: Frederic Weisbecker <fweisbec@...il.com>
	Date:   Wed Feb 3 09:09:33 2010 +0100

	perf lock: Drop the buffers multiplexing dependency

But this is not in -rc1, you need to checkout tip/perf/core

Well, the best would be you actually pull this on top of -rc1:

git://git.kernel.org/pub/scm/linux/kernel/git/frederic/random-tracing.git
	perf/core

so that you get the buffers multiplexing dependency that is in -tip,
and you also get the recursions fixes, not yet in -tip (but should make
it soon).

I bet you still won't have magic results after that, but still it should
be better.

We still have further projects in mind to improve the scalability,
like the events injection thing (that avoids the string copy)

Again, you are my eyes on this, I'm still blind with my poor dual
laptop or my atom testbox.

Thanks for your testing.

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