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

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Date:	Thu, 5 Apr 2007 21:11:29 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	David Howells <dhowells@...hat.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	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)


* 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. 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.

	Ingo

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