Subject: Re: 2.6.13-rc6-rt9
From: Thomas Gleixner <tglx@linutronix.de>
Reply-To: tglx@linutronix.de
To: paulmck@us.ibm.com
Cc: George Anzinger <george@mvista.com>,
       Peter Zijlstra <a.p.zijlstra@chello.nl>, Ingo Molnar <mingo@elte.hu>,
       linux-kernel@vger.kernel.org, Steven Rostedt <rostdt@goodmis.org>,
       Jeff Dike <jdike@addtoit.com>
In-Reply-To: <20050930010041.GS8177@us.ibm.com>
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	 <1127980463.14695.6.camel@twins>  <20050930010041.GS8177@us.ibm.com>
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Organization: linutronix
Date: Fri, 30 Sep 2005 03:07:29 +0200
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On Thu, 2005-09-29 at 18:00 -0700, Paul E. McKenney wrote:
> > Even with a current -rt (2.6.14-rc2-rt5) UML does not run. The issue is
> > indeed (as jeff pointed out) that VTALRM is never send. The small test
> > programm below illustrates this.
> > 
> > On a non-rt kernel it completed in 1 second.
> > On a -rt kernel it waits at infinitum.
> 
> Will play with it and see what I broke...

Paul, 

you are not the culprit :)

The run_posix_cpu_timers(p) call is #ifdef'd out with PREEMPT_RT. 

Thats a hard to fix issue. 

It can not be run from hardirq context, as it takes a lot of locks
(especially our favorites: tasklist_lock and sighand->siglock). :(

Maybe another playground for rcu, but it might also be solved by some
other mechanism for accounting and delayed execution in the PREEMPT_RT
case.

tglx


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