Subject: Re: [PATCH] gettimeofday stability

From: Samuel Rydh <[email-masked]>
Date: Thu, 19 Apr 2001 22:43:32 +0200

On Mon, Apr 16, 2001 at 01:25:56PM +0200, Gabriel Paubert wrote:
> > Ideally, TB should not be touched. Indeed, MOL can run without
> > touching TB (but DEC is essential). However, TB needs to be
> > modified for 'save session' feature to work. Basically, the RAM
> > and cpu state of MacOS is flushed to disk. At a later time,
> > MacOS can be restarted instantly. The problem is that MacOS can't
> > deal with the TB skip that occurs if the timebase is not restored
> > (no big surprise there).
>
> By touching the TB, you'll also break all other Linux applications which
> may have a valid use for the TB.

The only noticeable effect is a small clock drift originating from
the loading and restoring of the timebase (and of course, only when
MOL is running). Whatever MOL puts into TB/DEC is completely
invisible to other processes.

Anyway, I'll see if I can locate and patch away the use of
the timebase register in MacOS - that would allow the
save-session feature to work without having to touch the TB.

> BTW: how do you handle multiple MOL sessions ?

Mutli-session support was actually added a few days ago -
a matter of making sure the MOL kernel module keeps session
specific data in a single struct, passed as a parameter.

> > Anyway, the negative offset check is desirable even if it is
> > only the DEC that is touched.
>
> No, it is not, is is a textbook case of curing the symptom instead of the
> cause.

Well, what I was looking for was a change to remove the assumption
that the timer code was the sole user of the DEC register. Pauls
change seems fix that neatly.

Regards,

/Samuel

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