Re: i386/RTC: old problem, new solution?

Richard Gooch (rgooch@atnf.csiro.au)
Fri, 21 May 1999 00:16:47 +1000

Ulrich Windl writes:
> On 20 May 99, at 23:41, Richard Gooch wrote:
>
> > Riley Williams writes:
>
> [...]
>
> > > Unfortunately, it's already been dealt with in userspace, so any
> > > kernel patch you developed would be unlikely to be applied anyway.
> >
> > In fact, there already is a patch in the kernel:
> > CONFIG_APM_RTC_IS_GMT, but it's a temporary hack, until a better
> > scheme is implemented. The reason is that the kernel needs to know the
> > timezone the RTC is stored in when restoring the system clock after a
> > suspend/resume cycle. Automatically computing the difference has its
> > problems.
>
> Maybe you'll agree that akernel parameter is probably better than a
> compilation parameter. For distributions it will make things much
> easier.

As I said, what's in there now is a hack. A kernel parameter would be
an improvement. For the purposes of suspend/resume, it's preferable to
have a safe algorithm which determines the offset between the system
clock and the RTC. The old algorithm needs to read the RTC after the
suspend event is caught (but before the kernel allows/denys the
suspend). The problem is that the Dell Inspiron 3200 slows down the
system even before the kernel can allow the suspend event. This makes
the RTC measurement take several seconds.

Even without the Inspiron problem, you get up to 1 second error. This
accumulates for every suspend/resume cycle. Close and open your laptop
10 times a day and you lose 10 seconds a day. Stephen is working on a
better measurement algorithm.

The only place I'm aware that the kernel needs to know the timezone is
this case with suspend/resume. So aside from this, I don't see a need
for the kernel to know the timezone. Hm. Although I vaguely remember
something about SMB and timestamps. Stupid M$. Probably a good reason
for pushing SMBFS into user space. It's not really that important
anyway </flamebait>.

Regards,

Richard....

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