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Date: Fri, 29 May 2009 01:40:11 +0900
From: Paul Mundt <lethal@linux-sh.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Daniel Walker <dwalker@fifo99.com>, Thomas Gleixner <tglx@linutronix.de>,
       Linus Walleij <linus.ml.walleij@gmail.com>, Ingo Molnar <mingo@elte.hu>,
       Andrew Victor <linux@maxim.org.za>,
       Haavard Skinnemoen <hskinnemoen@atmel.com>,
       Andrew Morton <akpm@linux-foundation.org>, linux-kernel@vger.kernel.org,
       linux-sh@vger.kernel.org, linux-arm-kernel@lists.arm.linux.org.uk,
       John Stultz <johnstul@linux.vnet.ibm.com>
Subject: Re: [PATCH] sched: Support current clocksource handling in fallback sched_clock().
Message-ID: <20090528164011.GA30104@linux-sh.org>
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	John Stultz <johnstul@linux.vnet.ibm.com>
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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.