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Date: Sat, 11 Jun 2005 20:15:28 +0200
From: Ingo Molnar <mingo@elte.hu>
To: Karim Yaghmour <karim@opersys.com>
Cc: Kristian Benoit <kbenoit@opersys.com>, linux-kernel@vger.kernel.org,
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Subject: Re: PREEMPT_RT vs ADEOS: the numbers, part 1
Message-ID: <20050611181528.GA15019@elte.hu>
References: <42AA6A6B.5040907@opersys.com> <20050611070845.GA4609@elte.hu> <42AAF5CE.9080607@opersys.com> <20050611145240.GA10881@elte.hu> <42AB2209.9080006@opersys.com>
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* Karim Yaghmour <karim@opersys.com> wrote:

> Here's the .config for 2.6.12-rc4-RT-V0.7.47-08:

Thanks. These PREEMPT_RT debugging features should be disabled:

> CONFIG_DEBUG_PREEMPT=y
> CONFIG_WAKEUP_TIMING=y
> CONFIG_PREEMPT_TRACE=y
> CONFIG_LATENCY_TIMING=y
> CONFIG_RT_DEADLOCK_DETECT=y

they all cause significant overhead.

I'd also disable these two security options:

> CONFIG_AUDIT=y
> CONFIG_SECURITY=y

unless you are running an selinux-enabled environment.

i've had not that good experiences with HPET:

> CONFIG_HPET_TIMER=y
> CONFIG_HPET_EMULATE_RTC=y

so i'd disable it - but YMMV.

i'd also disable PAE and use CONFIG_NOHIGHMEM:

> CONFIG_HIGHMEM64G=y

unless you have more than 4GB of RAM. (if you have between 1GB and 4GB 
then use HIGHMEM4G)

then i'd disable stack-overflow checking as well:

> CONFIG_DEBUG_STACKOVERFLOW=y
> CONFIG_DEBUG_STACK_USAGE=y

since you are not running 4K stacks.

	Ingo