linux-kernel - Re: [PATCH] RFC: nomadik: expand timesource to 63 bits

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Message-id: <alpine.LFD.2.00.1011121416440.13911@xanadu.home>
Date:	Fri, 12 Nov 2010 14:18:12 -0500 (EST)
From:	Nicolas Pitre <nico@...xnic.net>
To:	Linus Walleij <linus.walleij@...ricsson.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>,
	john stultz <johnstul@...ibm.com>,
	Rabin VINCENT <rabin.vincent@...ricsson.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Colin Cross <ccross@...gle.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] RFC: nomadik: expand timesource to 63 bits

On Fri, 12 Nov 2010, Linus Walleij wrote:

> Thomas Gleixner wrote:
> > On Fri, 12 Nov 2010, Linus Walleij wrote:
> >> Uwe Kleine-König 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