Message-ID: <4846F789.7050702@qualcomm.com>
Date: Wed, 04 Jun 2008 13:14:01 -0700
From: Max Krasnyansky <maxk@qualcomm.com>
User-Agent: Thunderbird 2.0.0.14 (X11/20080501)
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To: Peter Zijlstra <a.p.zijlstra@chello.nl>
CC: Dimitri Sivanich <sivanich@sgi.com>, linux-kernel@vger.kernel.org,
       Ingo Molnar <mingo@elte.hu>, Nick Piggin <nickpiggin@yahoo.com.au>,
       rostedt@goodmis.org, Oleg Nesterov <oleg@tv-sign.ru>,
       "Paul E. McKenney" <paulmck@us.ibm.com>,
       Paul Menage <menage@google.com>, "Randy.Dunlap" <rddunlap@osdl.org>,
       suresh.b.siddha@intel.com
Subject: Re: Stop machine threads are getting preemted by the rt	period	enforcement
References: <20080601213019.14ea8ef8.pj@sgi.com>	 <20080602164203.GA2477@sgi.com> <48443E66.6060205@qualcomm.com>	 <20080602214151.GA7072@sgi.com> <48446D46.2010903@qualcomm.com>	 <20080603144010.GA25948@sgi.com> <20080604140036.GC18993@sgi.com>	 <4846D9FE.4030804@qualcomm.com>	 <1212603506.19205.2.camel@lappy.programming.kicks-ass.net>	 <4846DDC1.1050203@qualcomm.com> <1212605725.19205.17.camel@lappy.programming.kicks-ass.net>
In-Reply-To: <1212605725.19205.17.camel@lappy.programming.kicks-ass.net>
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Peter Zijlstra wrote:
> 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.

Oh, I did not realize that rt period is a timer that iterates online cpus. I
assumed that you do it in the scheduler tick or something.

Max
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