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Date: Fri, 23 Nov 2007 22:44:04 +0100
From: Kris Kennaway <kris@FreeBSD.org>
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To: Joseph Koshy <joseph.koshy@gmail.com>
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Cc: Attilio Rao <attilio@freebsd.org>, freebsd-stable@freebsd.org,
	Alexey Popov <lol@chistydom.ru>
Subject: Re: 2 x quad-core system is slower that 2 x dual core on FreeBSD
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Joseph Koshy wrote:
>>> Also I tried to find what else is slow in FreeBSD, I tried hwpmc as
>>> module and in kernel, but it fails with error:
>>> pmc: Unknown Intel CPU.
>>> module_register_init: MOD_LOAD (hwpmc, 0xffffffff804833e0,
>>> 0xffffffff809338a0) error 78
> 
>> There are patches you need to enable it on woodcrest.  They are in my p4
>> branch (kris-contention) but I don't have time right now to extract them.
> 
> These patches make hwpmc treat these CPUs are possessing Pentium-Pro class
> PMCs.
> 
> Unfortunately, this is easy to do, but incorrect:
> - There are differences in the legal bit values that may be loaded into
>   PMC registers for many hardware events.
> - hwpmc needs to be taught to support measurements on CPUs with
>   multiple cores per package.
> 
> And then there is additional work to support these CPUS
> at the same level as the current set:
> - The hardware events supported are named differently; documentation,
>    libpmc's event selector parsing code need to be changed to suit.
> - The hardware supports a new class of "fixed function" PMCs that
>    hwpmc needs to support.
> 

Well, this is all true, but overlooks the point that it does minimally 
work, which is of critical importance to people with one of these CPUs 
who want to actually use your tool ;)

Kris