linux-kernel - Re: [PATCH V7 1/8] ntp: add ADJ

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Message-ID: <20101223061359.GA7169@riccoc20.at.omicron.at>
Date:	Thu, 23 Dec 2010 07:13:59 +0100
From:	Richard Cochran <richardcochran@...il.com>
To:	"Kuwahara,T." <6vvetjsrt26xsrzlh1z0zn4d2grdah@...il.com>
Cc:	john stultz <johnstul@...ibm.com>, linux-kernel@...r.kernel.org,
	linux-api@...r.kernel.org, netdev@...r.kernel.org,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Arnd Bergmann <arnd@...db.de>,
	Christoph Lameter <cl@...ux.com>,
	David Miller <davem@...emloft.net>,
	Krzysztof Halasa <khc@...waw.pl>,
	Peter Zijlstra <peterz@...radead.org>,
	Rodolfo Giometti <giometti@...ux.it>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH V7 1/8] ntp: add ADJ_SETOFFSET mode bit

On Thu, Dec 23, 2010 at 05:27:58AM +0900, Kuwahara,T. wrote:
> On Wed, Dec 22, 2010 at 7:25 AM, john stultz <johnstul@...ibm.com> wrote:
> > I don't see why that would be better then adding a
> > clear new mode flag?
> 
> In short, time step is a special case of time slew.  Those are the same,
> only different in one parameter, as is shown in my previous post.
> That's why I said there's no need for adding a new mode.

Well, in addition to the objections raised by John, your suggested
implementation is also shortsighted. The field timex.constant is
copied into time_constant in some code paths. Obviously, this would be
a bad thing when timex.constant==-huge.

So, you need to clarify the interaction between ADJ_OFFSET,
ADJ_TIMECONST, ADJ_TAI, timex.constant, time_constant, and MAXTC.

If you would fully implement your idea, I expect it would become
obvious that it a bit of a hack, both in the kernel code and in the
user space interface. But, if you disagree, please just post a patch
with the complete implementation...

Thanks,
Richard
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