2 x quad-core system is slower that 2 x dual core on FreeBSD

Joseph Koshy joseph.koshy at gmail.com
Fri Nov 23 04:09:48 PST 2007

> > 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

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.

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