question about Intel P4 versus Alpha's

[Nathan Fredrickson]

Daniel Kidger wrote:
>
> In general, people prefer to switch off hyperthreading for HPC clusters,
> either via a BIOS option, or by passing 'noht' to the kernel (in say
> grub.conf).
>

Why is HT off preferred for HPC clusters?  I know it is beneficial to
disable HT until you upgrade to a kernel that has an HT aware scheduler
(either a patch to 2.4.19 or the upcoming O1 scheduler in 2.5).  Is that the
reason here, or is there another reason to not use HT in a HPC cluster?

Nathan