Re: Extreme system overhead on large IP27

[Ralf Baechle <ralf@linux-mips.org>]

On Wed, Oct 25, 2006 at 02:34:28AM +0900, Atsushi Nemoto wrote:
> Date:	Wed, 25 Oct 2006 02:34:28 +0900 (JST)
> To:	ralf@linux-mips.org
> Cc:	creideiki+linux-mips@ferretporn.se, linux-mips@linux-mips.org
> Subject: Re: Extreme system overhead on large IP27
> From:	Atsushi Nemoto <anemo@mba.ocn.ne.jp>
> Content-Type: Text/Plain; charset=us-ascii
> 
> On Tue, 24 Oct 2006 16:50:45 +0100, Ralf Baechle <ralf@linux-mips.org> wrote:
> > > 2. Timekeeping is broken. The clock in /proc/driver/rtc seems correct, but
> > > the system clock advances at about 1/16 of real time.
> > 
> > This one was caused by changeset ebca9aafa9bd5086d9f310205a8e30e225c5a5a6
> > which apparently wasn't quite ripe.  You can work around it by
> > revoking this changeset for now.  The time damage affects other systems
> > as well ...
> 
> Now I'm looking my patch again but still can not find any problem...
> 
> One question:
> 
> >    # zcat /proc/config.gz | grep HZ | grep -v ^#
> >    CONFIG_HZ_250=y
> >    CONFIG_SYS_SUPPORTS_ARBIT_HZ=y
> >    CONFIG_HZ=250
> 
> IP27 really supports HZ=250 ?

Arbitrary frequency actually.  The timer used is the HUB timer which is
running at 800ns afair.  It's like 53 bits or so.  There is also a compare
register so it's somewhat similar to the cop0 counter / compare timer.

  Ralf