linux-kernel - Re: [PATCH] kthread: always create the kernel threads with normal priority

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Message-ID: <20080108105428.2fb04bdd@brian.englab.brq.redhat.com>
Date:	Tue, 8 Jan 2008 10:54:28 +0100
From:	Michal Schmidt <mschmidt@...hat.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Jon Masters <jcm@...hat.com>,
	Satoru Takeuchi <takeuchi_satoru@...fujitsu.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCH] kthread: always create the kernel threads with normal
 priority

On Mon, 7 Jan 2008 09:29:56 -0800
Andrew Morton <akpm@...ux-foundation.org> wrote:

> On Mon, 7 Jan 2008 12:09:04 +0100 Ingo Molnar <mingo@...e.hu> wrote:
> 
> > 
> > > > This causes a practical problem. When a runaway real-time task
> > > > is eating 100% CPU and we attempt to put the CPU offline,
> > > > sometimes we block while waiting for the creation of the
> > > > highest-priority "kstopmachine" thread.
> > 
> > sched-devel.git has new mechanisms against runaway RT tasks.
> > There's a new RLIMIT_RTTIME rlimit - if an RT task exceeds that
> > rlimit then it is sent SIGXCPU.
> 
> Is that "total RT CPU time" or "elapsed time since last schedule()"?
> 
> If the former, it is not useful for this problem.

It's "runtime since last sleep" so it is useful.

I still think the kthread patch is good to have anyway. The user can
have other reasons to change kthreadd's priority/cpumask.

Michal
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