linux-kernel - Re: [PATCH NET-NEXT 01/10] clocksource: allow usage independent of timekeeping.c

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Message-Id: <1233782100.6994.82.camel@localhost.localdomain>
Date:	Wed, 04 Feb 2009 13:15:00 -0800
From:	john stultz <johnstul@...ibm.com>
To:	Daniel Walker <dwalker@...o99.com>
Cc:	Patrick Ohly <patrick.ohly@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	David Miller <davem@...emloft.net>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH NET-NEXT 01/10] clocksource: allow usage independent of
	timekeeping.c

On Wed, 2009-02-04 at 13:04 -0800, Daniel Walker wrote:
> On Wed, 2009-02-04 at 12:06 -0800, john stultz wrote:
> 
> > The duplication is only at a very low level. He could not reuse the
> > established clocksource system without really breaking its semantics.
> 
> He gave a link to the first version,
> 
> http://kerneltrap.org/mailarchive/linux-netdev/2008/11/19/4164204
> 
> What specific semantics is he breaking there? 

His re-usage of cycle_last and xtime_nsec for other means then how
they're defined.

In that case his use of xtime_nsec doesn't even store the same unit.

Plus he adds other accessors to the clocksource structure that are not
compatible with the clocksources registered for timekeeping.

He's really doing something different here, and while it does access a
counter, and it does translate that into nanoseconds, its not the same
as whats done in the timekeeping core which the clocksource was designed
around.

So by creating his own infrastructure in a shared manner, splitting out
a chunk of it to be reused in the clocksource/timekeeping core I think
is really a good thing and the right approach.

thanks
-john

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