linux-kernel - Re: [PATCH RFC] perf lock: Add new event "lock_acquired

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Date:	Mon, 02 Aug 2010 14:23:04 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Hitoshi Mitake <mitake@....info.waseda.ac.jp>
Cc:	Frederic Weisbecker <fweisbec@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	linux-kernel@...r.kernel.org, h.mitake@...il.com,
	Ingo Molnar <mingo@...e.hu>, Paul Mackerras <paulus@...ba.org>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Jason Baron <jbaron@...hat.com>,
	Xiao Guangrong <xiaoguangrong@...fujitsu.com>,
	Jens Axboe <axboe@...nel.dk>
Subject: Re: [PATCH RFC] perf lock: Add new event "lock_acquired_waittime"
 for contention analysis

On Sun, 2010-08-01 at 14:36 +0900, Hitoshi Mitake wrote:
> I want to make lockdep production kernel feature with dynamic
> patching.

Not really feasible. Note that enabling lockdep grows the size of
spinlock_t (and others) quite significantly.

Then there is the problem that you need to pass all tasks through some
quiesent state in order to enable lockdep (there must be a guarantee of
no locks held).

Now, we could possibly make it all work, but I'm not at all convinced we
want to pay the price, which is a much _much_ more complex
infrastructure.

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