linux-kernel - Re: [PATCH] sched: Support current clocksource handling in fallback sched

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Date:	Thu, 28 May 2009 19:00:30 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Daniel Walker <dwalker@...o99.com>
cc:	Paul Mundt <lethal@...ux-sh.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Linus Walleij <linus.ml.walleij@...il.com>,
	Ingo Molnar <mingo@...e.hu>,
	Andrew Victor <linux@...im.org.za>,
	Haavard Skinnemoen <hskinnemoen@...el.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-sh@...r.kernel.org,
	linux-arm-kernel@...ts.arm.linux.org.uk,
	John Stultz <johnstul@...ux.vnet.ibm.com>
Subject: Re: [PATCH] sched: Support current clocksource handling in fallback
 sched_clock().

On Thu, 28 May 2009, Daniel Walker wrote:
> > > > 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. 

That does not matter at all. If we have an unregister call then we
have to be prepared for 

     - the memory which contained the clocksource is freed 
     - the underlying hardware is going away. 

It does not matter at all if that happens in a compiled in or in a
modular driver.

Thanks,

	tglx
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