Date: Tue, 28 Mar 2006 19:21:37 -0600
From: Matt Mackall <mpm@selenic.com>
To: Alessandro Zummo <alessandro.zummo@towertech.it>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>, Andi Kleen <ak@muc.de>,
       akpm@osdl.org, torvalds@osdl.org, davem@davemloft.net,
       kkojima@rr.iij4u.or.jp, lethal@linux-sh.org, paulus@samba.org,
       ralf@linux-mips.org, rmk@arm.linux.org.uk, linux-kernel@vger.kernel.org
Subject: Re: 11 minute RTC update (was Re: Remove RTC UIP)
Message-ID: <20060329012137.GB3642@waste.org>
References: <200603270920.k2R9KYYx007214@shell0.pdx.osdl.net> <20060327111836.GA79131@muc.de> <20060327163218.GD3642@waste.org> <20060327190037.GB27030@muc.de> <20060327211143.55ef7c4e@inspiron> <1143512075.2284.2.camel@localhost.localdomain> <20060329000215.683eb2d5@inspiron> <20060329000345.GZ3642@waste.org> <20060329031102.0e056d85@inspiron>
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On Wed, Mar 29, 2006 at 03:11:02AM +0200, Alessandro Zummo wrote:
> On Tue, 28 Mar 2006 18:03:45 -0600
> Matt Mackall <mpm@selenic.com> wrote:
> 
> > > > >  While we are on the topic, I would like to ask everyone about
> > > > >  the 11 min ntp/rtc update feature of the kernel.
> > > > > 
> > > > >  It is something that makes sense to move to
> > > > >  userland?
> > > > 
> > > > YES !!! :)
> > > 
> > >  great! given that it is not implemented in the new RTC subsystem
> > >  and nobody objected, I will not add it :)
> > 
> > I agree that this should be migrated to userspace, but I'm more
> > worried about the functionality impact here than for the UIP case.
> > 
> > With existing NTP setups, and the kernel no longer writing to the RTC,
> > you might have the RTC drift far enough that NTP failed to sync on the
> > next boot. (Correct me if I'm wrong, of course.)
> 
>  That's probably true, I'm not expert on the matter. The new subsystem only
>  covers platforms that were not covered before (i.e. without external patches),
>  so that this should not impact users because the NTP update mode
>  was not working on them.
> 
>  The problem might arise when other RTC drivers (i.e. x86) will be converted
>  and deployed.
> 
>  We need a migration plan. Any suggestion? 

I guess the question then becomes: is existing userspace (ntpd)
already doing its own updates. If so, we can schedule the feature for
removal in the near future. If not, it may take quite a bit longer.

-- 
Mathematics is the supreme nostalgia of our time.
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