linux-kernel - Re: [PATCH 00/12] perf lock: New subcommand "perf lock", for analyzing lock statistics

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Date:	Fri, 22 Jan 2010 17:52:49 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Jason Baron <jbaron@...hat.com>
Cc:	Hitoshi Mitake <mitake@....info.waseda.ac.jp>,
	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
	Paul Mackerras <paulus@...ba.org>,
	Tom Zanussi <tzanussi@...il.com>,
	Steven Rostedt <srostedt@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Greg Kroah-Hartman <gregkh@...e.de>
Subject: Re: [PATCH 00/12] perf lock: New subcommand "perf lock", for
 analyzing lock statistics

On Fri, 2010-01-22 at 17:48 +0100, Peter Zijlstra wrote:
> On Fri, 2010-01-22 at 11:42 -0500, Jason Baron wrote:
> > On Fri, Jan 22, 2010 at 10:39:01PM +0900, Hitoshi Mitake wrote:
> > > Adding new subcommand "perf lock" to perf.
> > > 
> > 
> > looks like a really intresting patch! Does this patch mean that we can
> > potentially remove CONFIG_LOCK_STAT, now that the functionality is
> > available via 'perf'? Another desire for me has been to able to run
> > lockstat on production box. This has not been possible before without
> > incurring the performance penalty of lockdep. however, with 'perf' tools
> > ability to be turned on an off, perhaps there is (or we can build) a
> > mode for lockdep that is lower overhead for this usecase?
> 
> boot with: prove_locking=0
> 
> This patch still needs all the hooks and bits from lockdep, no way you
> want all that in a prodction kernel.

Also, I suspect lockstat to still be lots faster, since it doesn't need
to transfer gobs of data but builds the histogram in-kernel.

Having the ability to do in-kernel histrograms with perf is something
I've thought about but not yet managed to think of a nice way of doing
it.

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