linux-kernel - [BUG+PATCH] RT-Preempt: IRQ threads running at prio 0 SCHED

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Date:	Tue, 19 Dec 2006 21:52:42 +0100
From:	"Remy Bohmer" <l.pinguin@...il.com>
To:	"Ingo Molnar" <mingo@...e.hu>, linux-kernel@...r.kernel.org
Subject: [BUG+PATCH] RT-Preempt: IRQ threads running at prio 0 SCHED_OTHER

Hello Ingo,

I am using your yum-distributed kernel 2.6.19.1-rt15, and
unfortunately I experienced very worse latencies.
It turned out that ALL the IRQ threads were all running at prio 0, SCHED_OTHER.

Looking at the current code in kernel/irq/manage.c, the goal was to
put them at MAX_RT_PRIO, but the call to sys_sched_setscheduler()
fails with EINVAL. I have attached a patch to set them to
(MAX_RT_PRIO-1). This works.

Further I believe that each application of the RT-kernel requires a
different configuration of these thread-priorities and I prefer to
reconfigure these prios from userland during boot. As these
threadnames contain whitespaces in its name, they make the
shell-scripts unnecessary complex that I use to reconfigure the thread
priorities.
So, I would prefer a slight modification of the names: The attached
patch also changes the names from [IRQ nn] to [IRQ-nn]. I hope that
you agree with me here. (If not, I stick to do this patch each time
myself ;-) )

Kind Regards,

Remy Böhmer

Download attachment "fix-kernel-irq-thread-prio.patch" of type "application/octet-stream" (803 bytes)