linux-kernel - Re: preemption and rwsems (was: Re: missing madvise functionality)

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Message-Id: <20070405133742.88abc4f8.akpm@linux-foundation.org>
Date:	Thu, 5 Apr 2007 13:37:42 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	David Howells <dhowells@...hat.com>,
	Jakub Jelinek <jakub@...hat.com>,
	Ulrich Drepper <drepper@...hat.com>,
	Andi Kleen <andi@...stfloor.org>,
	Rik van Riel <riel@...hat.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	linux-mm@...ck.org, Hugh Dickins <hugh@...itas.com>
Subject: Re: preemption and rwsems (was: Re: missing madvise functionality)

On Thu, 5 Apr 2007 21:11:29 +0200
Ingo Molnar <mingo@...e.hu> wrote:

> 
> * David Howells <dhowells@...hat.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
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