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Date: Thu, 5 Apr 2007 13:37:42 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: Ingo Molnar <mingo@elte.hu>
Cc: David Howells <dhowells@redhat.com>, Jakub Jelinek <jakub@redhat.com>,
       Ulrich Drepper <drepper@redhat.com>, Andi Kleen <andi@firstfloor.org>,
       Rik van Riel <riel@redhat.com>,
       Linux Kernel <linux-kernel@vger.kernel.org>, linux-mm@kvack.org,
       Hugh Dickins <hugh@veritas.com>
Subject: Re: preemption and rwsems (was: Re: missing madvise functionality)
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On Thu, 5 Apr 2007 21:11:29 +0200
Ingo Molnar <mingo@elte.hu> wrote:

> 
> * David Howells <dhowells@redhat.com> wrote:
> 
> > But short of recording the lock sequence, I don't think there's anyway 
> > to find out for sure.  printk probably won't cut it as a recording 
> > mechanism because its overheads are too great.
> 
> getting a good trace of it is easy: pick up the latest -rt kernel from:
> 
> 	http://redhat.com/~mingo/realtime-preempt/
> 
> enable EVENT_TRACING in that kernel, run the workload 
> and do:
> 
> 	scripts/trace-it > to-ingo.txt
> 
> and send me the output.

Did that - no output was generated.  config at
http://userweb.kernel.org/~akpm/config-akpm2.txt

> It will be large but interesting. That should 
> get us a whole lot closer to what happens. A (much!) more finegrained 
> result would be to also enable FUNCTION_TRACING and to do:
> 
> 	echo 1 > /proc/sys/kernel/mcount_enabled
> 
> before running trace-it.

Did that - still no output.

I did get an interesting dmesg spew:
http://userweb.kernel.org/~akpm/dmesg-akpm2.txt