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

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Date:	Thu, 28 May 2009 20:44:28 +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:
> On Fri, 2009-05-29 at 02:53 +0900, Paul Mundt wrote:
> 
> > As I already stated, yes.
> > 
> > We have multiple clock sources for most CPUs. These can be set up in any
> > sort of configuration, and there are pros and cons to using different
> > ones. The ones that are available can in turn be cycled between. I don't
> > know what exactly is difficult to understand about this.
> 
> I understand that cpu's can have multiple clocks, that's not a hard concept to grasp.
> 
> > Yes, we want to be able to use modular clocksources. The only reason we
> > don't right now is because some more preparatory work is needed first.
> > Any attempt to remove support for modular clocksources means we will just
> > have to add it in back later.
> 
> This is what's difficult to understand.. You have multiple clocks ok,
> fine.. You have multiple clocks that you want the kernel to switch
> between, ok that's fine too.. What's missing is the case where
> clocksource modules being loaded/unload via the user becomes a valuable
> use case..

Did you actually read what people wrote ? This is not about modules or
not, it's about safe switching of clocksources when they are used for
sched_clock as well.
 
> If you have a valuable use case for that, fine, I won't stand in the
> way ..

Sigh,

	tglx
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