Subject: Re: [patch] Real-Time Preemption, -RT-2.6.12-rc2-V0.7.44-00
From: Steven Rostedt <rostedt@goodmis.org>
To: Rui Nuno Capela <rncbc@rncbc.org>
Cc: Ingo Molnar <mingo@elte.hu>, LKML <linux-kernel@vger.kernel.org>,
       Lee Revell <rlrevell@joe-job.com>
In-Reply-To: <46802.192.168.1.5.1112727980.squirrel@www.rncbc.org>
References: <20050325145908.GA7146@elte.hu> <20050331085541.GA21306@elte.hu>
	 <20050401104724.GA31971@elte.hu> <20050405071911.GA23653@elte.hu>
	 <46802.192.168.1.5.1112727980.squirrel@www.rncbc.org>
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Organization: Kihon Technologies
Date: Tue, 05 Apr 2005 15:36:02 -0400
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Our first victim!! :-) 

On Tue, 2005-04-05 at 20:06 +0100, Rui Nuno Capela wrote:
> >
> I'm having plenty of this on boot, on my SMP/HT desktop (P4/x86), while
> running RT-V0.7.44-01 (SMP+PREEMPT_RT):
> 
>   BUG: kstopmachine:xxxx RT task yield()-ing!
> 
> See sample dmesg and .config on attach.
> 
> OTOH, on my laptop (P4/UP), all seems to be clear fine.
> 

The kstopmachine is only run on SMP environments, so it won't show up on
your UP machine.


> Is this something to be affraid of? :)
> 

If your box is still running, then no.  But it's now a chore to remove
the yield from this algorithm, since yields have a possibility to
deadlock the system.  Although in this particular case, it may not be a
problem, since the threads that are being waited on are created for
other CPUs.  But I haven't looked too much into what stop_machine is
doing so I can very well be wrong.

Thank you for reporting it, we want to weed out all the yields that a RT
task may call.


-- Steve


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