linux-kernel - Re: [PATCH] lock stat for -rt 2.6.20-rc2-rt2 [was Re: 2.6.19-rt14 slowdown compared to 2.6.19]

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Date:	Sat, 30 Dec 2006 12:19:40 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Bill Huey <billh@...ppy.monkey.org>
Cc:	"Chen, Tim C" <tim.c.chen@...el.com>, linux-kernel@...r.kernel.org,
	"Siddha, Suresh B" <suresh.b.siddha@...el.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Steven Rostedt <rostedt@...dmis.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] lock stat for -rt 2.6.20-rc2-rt2 [was Re: 2.6.19-rt14 slowdown compared to 2.6.19]


* Bill Huey <billh@...ppy.monkey.org> wrote:

> On Tue, Dec 26, 2006 at 04:51:21PM -0800, Chen, Tim C wrote:
> > Ingo Molnar wrote:
> > > If you'd like to profile this yourself then the lowest-cost way of
> > > profiling lock contention on -rt is to use the yum kernel and run the
> > > attached trace-it-lock-prof.c code on the box while your workload is
> > > in 'steady state' (and is showing those extended idle times):
> > > 
> > >   ./trace-it-lock-prof > trace.txt
> >
> > Thanks for the pointer.  Will let you know of any relevant traces.
> 
> Tim,
> 	http://mmlinux.sourceforge.net/public/patch-2.6.20-rc2-rt2.lock_stat.patch
> 
> You can also apply this patch to get more precise statistics down to
> the lock. [...]

your patch looks pretty ok to me in principle. A couple of suggestions 
to make it more mergable:

 - instead of BUG_ON()s please use DEBUG_LOCKS_WARN_ON() and make sure 
   the code is never entered again if one assertion has been triggered.
   Pass down a return result of '0' to signal failure. See
   kernel/lockdep.c about how to do this. One thing we dont need are
   bugs in instrumentation bringing down a machine.

 - remove dead (#if 0) code

 - Documentation/CodingStyle compliance - the code is not ugly per se
   but still looks a bit 'alien' - please try to make it look Linuxish,
   if i apply this we'll probably stick with it forever. This is the
   major reason i havent applied it yet.

 - the xfs/wrap_lock change looks bogus - the lock is initialized
   already. What am i missing?

	Ingo
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