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Subject: Re: [PATCH] sched: Support current clocksource handling in
	fallback sched_clock().
From: Daniel Walker <dwalker@fifo99.com>
To: Paul Mundt <lethal@linux-sh.org>
Cc: Peter Zijlstra <peterz@infradead.org>,
       Thomas Gleixner <tglx@linutronix.de>,
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Date: Thu, 28 May 2009 09:52:27 -0700
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On Fri, 2009-05-29 at 01:40 +0900, Paul Mundt wrote:
> On Thu, May 28, 2009 at 06:32:09PM +0200, Peter Zijlstra wrote:
> > On Thu, 2009-05-28 at 09:13 -0700, Daniel Walker wrote:
> > > On Thu, 2009-05-28 at 14:59 +0200, Peter Zijlstra wrote:
> > > > CPU0                           CPU1
> > > > 
> > > > clock = ACCESS_ONCE(sched_clocksource);
> > > > 
> > > >                                unload module
> > > >                                  clocksource_unregister()
> > > >                                    sched_clocksource = jiffies
> > > >                                  unmap data/text
> > > > 
> > > > cyc2ns(clock, clocksource_read(clock)) <--- fireworks
> > > > 
> > > > 
> > > 
> > > Do any module based clocksources even exist right now?
> > > clocksource_unregister only seems to be used 3 times..
> > 
> > Good point, it appears its not even exported.
> > 
> > Thomas mentioned modules, I assumed.
> > 
> The drivers/clocksource/ drivers in theory could be modular anyways.
> Handling this transition properly is at least one less barrier to modular
> clocksources, so I think it's progress regardless. I don't remember what
> all of the other issues were though, John probably remembers.

I don't think it's an important case to consider right now ..
clocksources are usually so integral to the system putting one in a
module seems counterintuitive. 

Daniel