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

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Message-ID: <20100123065726.GA15774@elte.hu>
Date:	Sat, 23 Jan 2010 07:57:26 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Jason Baron <jbaron@...hat.com>,
	Hitoshi Mitake <mitake@....info.waseda.ac.jp>,
	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


* Peter Zijlstra <peterz@...radead.org> wrote:

> 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.

Yeah, that has come up in the past and it would be excellent to have. That 
would allow the removal of the special-purpose lockstat /proc output.

	Ingo
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