[cgl_discussion] CONFIG_HYPERTHREADING ??

Peter Badovinatz tabmowzo at us.ibm.com
Mon Oct 7 18:40:14 PDT 2002

"Randy.Dunlap" wrote:
> Hi,
> I was expecting to see something that implements CONFIG_HT or

Did you and Craig coordinate your posts ;) ?

Correct, the decision was to make it configurable.  We did not make a
statement specific to HOW to make this (or in general all of the)
requirement(s) actually configurable, although the discussion for this
one strongly implied that it would be able to be removed to the point of
not being available.  To follow the license issue, a vendor may want it
absolutely unavailable (i.e., compiled out) to prevent usage (accidental
or otherwise) if it were boot time set.

This issue in general would be another aspect necessary to be covered by
a certification suite, if we have configurable items what does that mean
and how do you certify them (or them not being there.)

An interesting follow-on, IMHO most distros will only test a much more
limited range of permutations of core+configurable items.  Are we going
to claim that we've built and/or tested similarly, or simply pick some
few (or 1?) combinations and identify those?

> * Requirements meeting minutes from 2002-08-26:
>  Hyperthreading
>  - already in kernel 2.4.19.
>  - Result:  Accept as Core in 1.0.1 with PROVISO:
>    - WITH PROVISO: that it can be configured out, even on hardware
>    platforms that support it.
>    - REASON: ISVs currently charge per-cpu, this makes it appear there
>    are more CPUs, so customers may not want it.  Also, some workloads
>    may not benefit from it.
>  AR: Khalid to asses work to make configurable, work with an Intel rep.
> * and Requirements meeting minutes from 2002-09-06:
>  Newly proposed items (i.e., going into Requirements 1.1):
>  Hyperthreading -- Core 1.1
>  UPDATE_0906: Move to Configurable 1.1 -- Platform-specific.
> * and OSDL CGL Requirements spec. v1.1:
>  Requirement: 2.8 Hyperthreading of CPUs
>  Version Assignment: Configurable 1.1
> Was I mistaken to be expecting this, or is this still an outstanding
> issue?
> Current status is that Hyperthreading can be disabled on the
> Linux kernel command line by using "noht" or can be disabled
> (usually) in the BIOS SETUP, but not as a kernel build option.
> This could easily be enough ways to disable it, but it's not
> matching the Requirements spec IMO.
> ###
> --
> ~Randy
>   "In general, avoiding problems is better than solving them."
>   -- from "#ifdef Considered Harmful", Spencer & Collyer, USENIX 1992.

Peter R. Badovinatz aka 'Wombat' -- IBM Linux Technology Center
preferred: tabmowzo at us.ibm.com / alternate: wombat at us.ibm.com
These are my opinions and absolutely not official opinions of IBM, Corp.

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