linux-kernel - Re: [RFC PATCH 09/12] clocksource: allow usage independent of timekeeping.c

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Message-Id: <1233759649.15940.209.camel@ecld0pohly>
Date:	Wed, 04 Feb 2009 16:00:49 +0100
From:	Patrick Ohly <patrick.ohly@...el.com>
To:	Daniel Walker <dwalker@...o99.com>
Cc:	John Stultz <johnstul@...ibm.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	David Miller <davem@...emloft.net>,
	"linux-api@...r.kernel.org" <linux-api@...r.kernel.org>
Subject: Re: [RFC PATCH 09/12] clocksource: allow usage independent of
	timekeeping.c

On Wed, 2009-02-04 at 14:29 +0000, Daniel Walker wrote:
> On Mon, 2008-12-15 at 08:26 -0800, John Stultz wrote:
> 
> > Nice. The cyclecounter struct can work as a good base that I can shift
> > the clocksource bits over to as I clean that up.
> > 
> > We will probably want to split this out down the road, but for now its
> > small enough and related enough that I think its fine in the
> > clocksource.h/c.
> > 
> > Also since Magnus has been working on it, does enable/disable accessors
> > in the cyclecounter struct make sense for your hardware as well?
> > 
> > Also the corner cases on overflows (how we manage the state, should
> > reads be deferred for too long) will need to be addressed, but I guess
> > we can solve that when it becomes an issue. Just to be clear: none of
> > the hardware you're submitting this round has wrapping issues? Or is
> > that not the case?
> 
> Why wouldn't this just use a clocksource directly and not register it
> with the timekeeping? The cyclecounter is just a subset of the
> clocksource ..

The very first revision of the patch did exactly that:
http://kerneltrap.org/mailarchive/linux-netdev/2008/11/19/4164204

The patch was smaller, but it also took some shortcuts (reusing fields
meant to be used in a different way) and added other unused fields to
the user of such an independent clocksource instance.

I agree with John that separate structures for different aspects of the
problem (abstract API for read-only access to hardware; converting cycle
counter into continuously increasing time counter) is the cleaner
approach.

-- 
Best Regards, Patrick Ohly

The content of this message is my personal opinion only and although
I am an employee of Intel, the statements I make here in no way
represent Intel's position on the issue, nor am I authorized to speak
on behalf of Intel on this matter.

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