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

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Date:	Thu, 28 May 2009 11:10:52 -0700
From:	Daniel Walker <dwalker@...o99.com>
To:	Paul Mundt <lethal@...ux-sh.org>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	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 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..

If you have a valuable use case for that, fine, I won't stand in the
way ..

Daniel

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