linux-kernel - Re: Stop machine threads are getting preemted by the rt period enforcement

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Message-Id: <1212605725.19205.17.camel@lappy.programming.kicks-ass.net>
Date:	Wed, 04 Jun 2008 20:55:25 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Max Krasnyansky <maxk@...lcomm.com>
Cc:	Dimitri Sivanich <sivanich@....com>, linux-kernel@...r.kernel.org,
	Ingo Molnar <mingo@...e.hu>,
	Nick Piggin <nickpiggin@...oo.com.au>, rostedt@...dmis.org,
	Oleg Nesterov <oleg@...sign.ru>,
	"Paul E. McKenney" <paulmck@...ibm.com>,
	Paul Menage <menage@...gle.com>,
	"Randy.Dunlap" <rddunlap@...l.org>, suresh.b.siddha@...el.com
Subject: Re: Stop machine threads are getting preemted by the rt
	period	enforcement

On Wed, 2008-06-04 at 11:24 -0700, Max Krasnyansky wrote:
> 
> Peter Zijlstra wrote:
> > On Wed, 2008-06-04 at 11:07 -0700, Max Krasnyansky wrote:
> >> Peter, Ingo,
> >>
> >> Take a look at the report below (came up during isolcpu= remove discussions).
> >>
> >> It looks like stop_machine threads are getting forcefully preempted because
> >> they exceed their RT quanta. It's strange because rt period is pretty long.
> >> But given that disabling rt period logic solves the issue the machine was not
> >> really stuck.
> > 
> > Yeah, I know, I'm already looking at this
> 
> I see. Does it look like a bug in the rt period logic ?
> Or did the stop_machine thread really run for a long time (in the report that
> you got that is) ?

looks like a fun race between refreshing the period and updating
cpu_online_map.



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