Date: Thu, 17 Feb 2005 21:11:45 +0100
From: Ingo Molnar <mingo@elte.hu>
To: Lee Revell <rlrevell@joe-job.com>
Cc: Philippe Elie <phil.el@wanadoo.fr>,
       linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: Oops with oprofile + RT preempt 2.6.11-rc2-RT-V0.7.37-01
Message-ID: <20050217201145.GA14706@elte.hu>
References: <1108274835.3739.2.camel@krustophenia.net> <20050213130058.GA566@zaniah> <20050213133020.GA16363@elte.hu> <1108670727.11411.6.camel@krustophenia.net>
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* Lee Revell <rlrevell@joe-job.com> wrote:

> 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.

yes - most of the overhead can be disabled, but not all. 1% CPU time
might sound alot but when compared against 10% (or more) tracing
overehad it's small. The least overhead comes from disabling tracing in
the .config.

	Ingo
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