Date: Thu, 30 Sep 2004 15:24:43 -0400 From: Ken Smith <kensmith@cse.Buffalo.EDU> To: Poul-Henning Kamp <phk@phk.freebsd.dk> Cc: Ken Smith <kensmith@FreeBSD.org> Subject: Re: cvs commit: src/sys/sparc64/sparc64 machdep.c Message-ID: <20040930192443.GE19077@electra.cse.Buffalo.EDU> In-Reply-To: <48971.1096571367@critter.freebsd.dk> References: <200409301438.i8UEcx89022771@repoman.freebsd.org> <48971.1096571367@critter.freebsd.dk>
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On Thu, Sep 30, 2004 at 09:09:27PM +0200, Poul-Henning Kamp wrote:
> In message <200409301438.i8UEcx89022771@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
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.
--
Ken Smith
- From there to here, from here to | kensmith@cse.buffalo.edu
there, funny things are everywhere. |
- Theodore Geisel |
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