linux-kernel - Re: [GIT PULL] omap changes for v2.6.39 merge window

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Date:	Mon, 04 Apr 2011 09:26:19 +0100
From:	Marc Zyngier <Marc.Zyngier@....com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Russell King - ARM Linux <linux@....linux.org.uk>, david@...g.hm,
	Nicolas Pitre <nico@...xnic.net>,
	Tony Lindgren <tony@...mide.com>,
	Catalin Marinas <catalin.marinas@....com>,
	lkml <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-arm-kernel@...ts.infradead.org,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...e.hu>,
	linux-omap@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	David Brown <davidb@...eaurora.org>,
	Detlef Vollmann <dv@...lmann.ch>
Subject: Re: [GIT PULL] omap changes for v2.6.39 merge window

On Mon, 2011-04-04 at 02:59 +0200, Arnd Bergmann wrote:

> Abstracting sched_clock() to be run-time selected is something that
> needs to be taken care of. Maybe we could have a generic sched_clock
> implementation that is written on top of clocksource instead of jiffies,
> and always select that on architectures that have a decent clocksource.
> Are there any platforms on ARM where that would be a bad idea? I believe
> the main reaons why they are separate is that on x86 you can use the TSC
> for sched_clock in many cases where you cannot use it for clocksource.

I've proposed a mechanism for a run-time selectable sched_clock()
implementation as part of my A15 timer patch set:
http://www.spinics.net/lists/arm-kernel/msg116891.html
and more specifically patches #10 and #11.

I'm not completely pleased with it (the fact that it embeds a copy of
the generic sched_clock() to be used as a default is properly ugly), but
maybe this could be used as a base for further discussion.

Cheers,

	M.
-- 
Reality is an implementation detail.


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