From owner-freebsd-hackers@FreeBSD.ORG  Fri Mar 18 16:38:27 2011
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From: Jung-uk Kim <jkim@FreeBSD.org>
To: Kostik Belousov <kostikbel@gmail.com>
Date: Fri, 18 Mar 2011 12:38:11 -0400
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Cc: freebsd-hackers@freebsd.org, Bruce Evans <brde@optusnet.com.au>,
	Andriy Gapon <avg@freebsd.org>, Maxim Dounin <mdounin@mdounin.ru>
Subject: Re: get_cyclecount(9) deprecation
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On Friday 18 March 2011 12:15 pm, Kostik Belousov wrote:
> On Fri, Mar 18, 2011 at 05:51:27PM +0200, Andriy Gapon wrote:
> > on 18/03/2011 15:56 Kostik Belousov said the following:
> > > On Fri, Mar 18, 2011 at 05:26:53PM +1100, Bruce Evans wrote:
> > > ...
> > >
> > >> - set cputicker() has some design bugs.  It assumes that the
> > >> tick frequency is the same across all CPUs, but the TSC is
> > >> per-CPU.  I have an old SMP system with CPUs of different
> > >> frequency that can demonstrate bugs from this.
> > >
> > > We definitely do not support configurations with different
> > > models of CPUs in SMP, this is what Simmetric is about.
> > > Different as in frequency or stepping.
> >
> > Are there any fundamental reasons for us to not support that
> > configuration in situations where hardware and BIOS (in x86 case)
> > happen to support it?
> >
> > I am personally more interested in non-uniform topologies like
> > one package having two cores and another having four.
>
> We do not handle CPU errata/quirks individually per-core. I think
> that we assume that all cores have the same stepping and thus
> require the same workarounds, if any, as BSP. Also, I think tsc
> calibration is done only on BSP, but I may be wrong there.

Yeah, it is just sad but that's what we do now.  Just for per-CPU 
ticker, however, it won't be too hard, though.

Jung-uk Kim