[RFC/PATCH 1/2] Basic generic time/clocksource code for PowerPC

[Paul Mackerras]

Gabriel Paubert writes:

> On Fri, Sep 07, 2007 at 12:41:38AM +1000, Paul Mackerras wrote:
> > This changes PowerPC to use the generic time infrastructure for
> > gettimeofday et al.  We register a clocksource which uses the timebase
> > register, or the RTC on the 601.
> > 
> > It also gets rid of the RTC update stuff.  IIRC we discussed removing
> > this some time ago but never actually did it.
> 
> So who will be in charge of updating the RTC now? The update 
> every 11 min is there to stay on x86(-64) it seems.

I had an impression that ntpd would do it, but that seems to be wrong.

I also have been unable to find where in the kernel source there is
code for x86[-64] to do the RTC updates.  Do you know where it is?

Doing the updates from timer_interrupt will no longer really be
suitable since it is not called at regular intervals any more.  The
best thing would be for the ntp code to set up a timer when it reaches
synchronization.

> Removing this will have strange side effects: as an example,
> your laptop clock will be good if it synchronized on NTP, 
> then you put it to sleep, disconnect the network and RTC read 
> on wake up returns a wrong value, giving wrong timestamps.

No, the suspend/resume code reads the RTC on both suspend and resume,
and advances xtime by the difference between the two readings.  So the
time might be out by up to a second after resume, but it shouldn't be
way off, assuming that your RTC is advancing at the right speed.

> As someone who has a network of tens of machines using
> NTP for synchornisation I think it is a very bad idea
> unless we have a replacement.

OK, but I think that doing it in timer_interrupt is the wrong place.

Paul.