Date: Wed, 11 Jun 2003 17:25:40 -0400 (EDT)
From: Zwane Mwaikambo <zwane@linuxpower.ca>
To: Artemio <artemio@artemio.net>
cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: SMP question
In-Reply-To: <200306112252.40979.artemio@artemio.net>
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References: <200306112043.11923.artemio@artemio.net> <3EE7852C.2050605@rackable.com>
 <200306112252.40979.artemio@artemio.net>
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On Wed, 11 Jun 2003, Artemio wrote:

> I'm building a hard real-time Linux (RTLinux) system on a 2x Xeon machine. If 
> I compile and run a 2.4.18 kernel with SMP support, rtlinux hangs the 
> machine. However, with SMP disabled, rtlinux and all it's hard-realtime 
> applications runs okay.

Sounds like an RTLinux bug, perhaps you should elaborate on that on the 
RTLinux mailing list.

> So, I have to deside between these two:
> 
>  - Run rtlinux and hard-realtime applications on a kernel without SMP support. 
> How much performance will I loose this way? Is SMP *THAT* critical? 

Depending on your load it could make a very significant difference.

>  - Run all tasks in a usual way, no hard realtime, but with SMP support.

If you have that option you didn't need hard realtime in the first place.

> Also, if I turn hyperthreading off, how will it influence the system with SMP 
> support? Without SMP support?

HT w/ SMP = You'll have to do your own tests with your applications
HT w/o SMP = Normal UP

	Zwane
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