From owner-freebsd-hackers@FreeBSD.ORG  Fri Mar 18 17:05:27 2011
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Date: Sat, 19 Mar 2011 04:05:23 +1100 (EST)
From: Bruce Evans <brde@optusnet.com.au>
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Cc: Kostik Belousov <kostikbel@gmail.com>, freebsd-hackers@freebsd.org,
	Jung-uk Kim <jkim@freebsd.org>, Maxim Dounin <mdounin@mdounin.ru>
Subject: Re: get_cyclecount(9) deprecation
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On Sat, 19 Mar 2011, Bruce Evans wrote:

> On Fri, 18 Mar 2011, Kostik Belousov wrote:
>> 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.
>
> ...
> Now there is even more asymmetry
> in core frequencies, with the hardware transiently slowing down or
> stopping cores independently, at least for cores in different packages.

Also, with virtualization, the virtualizer cannot reasonably even provide
an invariant TSC that runs at the same rate on all cores.  It should
provide an invariant TSC that claims to run at the same rate on all cores,
but then the cores cannot run at the same rate except on average,
since some of the cores will have to run the virtualizer some of the
time, and it is unreasonable to distribute the overhead for this evenly
except on average.

Bruce