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Date: Fri, 12 Nov 2010 14:18:12 -0500 (EST)
From: Nicolas Pitre <nico@fluxnic.net>
To: Linus Walleij <linus.walleij@stericsson.com>
Cc: Thomas Gleixner <tglx@linutronix.de>,
        =?ISO-8859-15?Q?Uwe_Kleine-K=F6nig?= 
	<u.kleine-koenig@pengutronix.de>,
        john stultz <johnstul@us.ibm.com>,
        Rabin VINCENT <rabin.vincent@stericsson.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Colin Cross <ccross@google.com>,
        "linux-arm-kernel@lists.infradead.org" 
	<linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH] RFC: nomadik: expand timesource to 63 bits
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On Fri, 12 Nov 2010, Linus Walleij wrote:

> Thomas Gleixner wrote:
> > On Fri, 12 Nov 2010, Linus Walleij wrote:
> >> Uwe Kleine-K?nig wrote:
> >>
> >>> Instead of implementing sched_clock for each architecture seperatly,
> >>> wouldn't it be nice to have a generic sched_clock that uses the
> >>> architecture's clocksource?  I tried to implement that some time ago,
> >>> but tglx shoot it down because of locking problems.
> >> I was and still am a big fan of this approach, I am willing to help
> >> testing it if you want to dust off this patch set...
> > 
> > sched_clock is not necessarily the same as the current clocksource.
> 
> IIRC Uwe:s approach was that if and only if you would want to use
> the clocksource for sched_clock() you provide a special flag on
> the clocksource, and it will be attempted to be used for sched_clock().
> 
> Incidentally the dual use of a single free-running timer as both
> single clocksource and sched_clock() baseline seem to creep up in
> a lot of embedded platforms...

Sure, but the computations and associated cost around that free running 
timer are not the same in both cases.


Nicolas

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