Subject: Re: Oops with oprofile + RT preempt 2.6.11-rc2-RT-V0.7.37-01
From: Lee Revell <rlrevell@joe-job.com>
To: Ingo Molnar <mingo@elte.hu>
Cc: Philippe Elie <phil.el@wanadoo.fr>,
       linux-kernel <linux-kernel@vger.kernel.org>
In-Reply-To: <20050213133020.GA16363@elte.hu>
References: <1108274835.3739.2.camel@krustophenia.net>
	 <20050213130058.GA566@zaniah>  <20050213133020.GA16363@elte.hu>
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Date: Thu, 17 Feb 2005 15:05:26 -0500
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On Sun, 2005-02-13 at 14:30 +0100, Ingo Molnar wrote:
> * Philippe Elie <phil.el@wanadoo.fr> wrote:
> 
> > oprofile_ops.cpu_type == NULL, this has been fixed 3 weeks ago, can
> > you retry with -rc4 ?
> 
> i've uploaded an -rc4 port of the -RT tree half an hour ago (-39-00).
> 

Thanks, -rc4 did fix the bug.

I noticed profiling the kernel with PREEMPT_DESKTOP that mcount and
__mcount add quite a bit of overhead.  Something like .5% CPU each.
Sorry, I didn't save the oprofile output.

So, disable CONFIG_MCOUNT if you want minimal overhead from the RT
patches.  IIRC it was previously stated that the latency tracing
overhead could be mostly avoided by disabling it at runtime.

Lee 

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