cvs commit: src/sys/sparc64/sparc64 machdep.c

[Marius Strobl]

On Thu, Sep 30, 2004 at 03:24:43PM -0400, Ken Smith wrote:
> On Thu, Sep 30, 2004 at 09:09:27PM +0200, Poul-Henning Kamp wrote:
> > In message <200409301438.i8UEcx89022771 at repoman.freebsd.org>, Ken Smith writes:
> > >kensmith    2004-09-30 14:38:59 UTC
> > >
> > >  FreeBSD src repository
> > >
> > >  Modified files:
> > >    sys/sparc64/sparc64  machdep.c 
> > >  Log:
> > >  This along with v1.6 of counter.c fixes some timecounter issues on
> > >  MP machines (hopefully).  CPU timers are OK on UP machines but we
> > >  don't keep the timers in sync on MP machines so if the CPU's timer
> > >  is chosen as the primary timecounter it's possible for time to
> > >  not be monotonically increasing because different CPU's counters
> > >  may be used at different times.  But the CPU's counters are otherwise
> > >  one of the higher quality counters available.  So, on UP machines
> > >  we'll use a relatively high quality value but on MP machines we'll
> > >  use a quality that should prevent the CPU's counters from being chosen.
> > 
> > The 'microsecond clock' is present in all suns so we don't leave any
> > machines without timecounters, right ?
> > 
> 
> Funny you should ask.  Testing the first version of this patch was how
> we found the bug in counter.c - the machine I booted the test kernel
> with happened to decide the counter-timer wasn't suitable either due
> to the bug and it came up with no timecounters.  You should see what
> happens to a machine that's not keeping time.  :-)
> 
> Marius has device maps for virtually all known Sparc hardware and
> he said all of the MP machines do have the counter-timer available

Well, that's an exaggeration :)
But I think I have enough to say that all Sun UltraSparc II boards
have a counter-timer device.

> in them.  Only the IIi and IIe processor based systems don't and
> they're only UP machines.
> 
> We are drastically low on timecounter-capable devices on sparc64
> though, it seems the counter-timer and the CPU are about all there
> is.
> 
> If this makes you nervous and if you have any suggestions I'm all
> ears.
>