linux-kernel - Re: [patch 3/3] Enable setting of IRQ-thread priorities from kernel cmdline. (repost:CC to LKML)

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Message-Id: <200712201418.17378.jbe@pengutronix.de>
Date:	Thu, 20 Dec 2007 14:18:16 +0100
From:	Juergen Beisert <jbe@...gutronix.de>
To:	linux-rt-users@...r.kernel.org
Cc:	"Jaswinder Singh" <jaswinderlinuxrt@...il.com>,
	"Remy Bohmer" <linux@...mer.net>,
	"Steven Rostedt" <rostedt@...dmis.org>,
	"Arnaldo Carvalho de Melo" <acme@...stprotocols.net>,
	"Ingo Molnar" <mingo@...e.hu>, "Darren Hart" <dvhltc@...ibm.com>,
	"Sven-Thorsten Dietrich" <sdietrich@...ell.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [patch 3/3] Enable setting of IRQ-thread priorities from kernel cmdline. (repost:CC to LKML)

On Thursday 20 December 2007 13:45, Jaswinder Singh wrote:
> On 12/20/07, Remy Bohmer <linux@...mer.net> wrote:
> > So, Is this a serious requirement? Should this be possible?
>
> I have noticed this problem:
> root@....168.1.253:~# cat /proc/loadavgrt
> 1.00 1.00 1.00 0/52 1158
> root@....168.1.253:~# cat /proc/loadavg
> 0.00 0.00 0.02 1/52 1159
> root@....168.1.253:~#
>
> So I am curious, if possible, user can switch softirq-threads or IRQs
> RT tasks to non-RT tasks for slow hardware or least important hardware
> for NON-RT tasks. So this will improve RT behaviour.
                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Why?

IMHO: Simply decrease the RT priority of less important IRQs or increase all 
other more important IRQs. IRQs are always more important than other 
processes in a system, also in non RT systems.

Juergen
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