Hyperthreading issues.

[kama]

On Sun, 13 Nov 2005, Doug White wrote:

> On Fri, 11 Nov 2005, kama wrote:
>
> > Just upgraded from 5.4 to 6.0 and hyperthreading stoped working.
> > Everything looks ok, but it doesn't use two of the logical CPU's.
>
> This is disabled by default due to a information-leak vulnerability across
> the hyperthreaded cores. The details from the release notes:
>
> Because of an information disclosure vulnerability on processors using
> Hyper-Threading Technology (HTT), the machdep.hyperthreading_allowed
> sysctl variable has been added. It defaults to 1 (HTT enabled) on FreeBSD
> CURRENT, and 0 (HTT disabled) on the 4-STABLE and 5-STABLE development
> branches and supported security fix branches. More information can be
> found in security advisory FreeBSD-SA-05:09.htt. [MERGED]
>
> If you don't care about this, add
>
> machdep.hyperthreading_allowed="1"
>
> to /boot/loader.conf and reboot.

If you had read the mail you'll see further down that its indeed set.

After a while it seems to use cpu2&3 but more rarely than 1&0, maybe its
ULE that makes it work that way.

>
> > One other thing is when I try to switch off hyperthreading in BIOS, it
> > will hang at bootup when it are settling the scsi drives. After awhile it
> > will give me scsi timeouts. This only happens when I have two cpu enabled
> > and hyperthreading off. If I disable one cpu w ht off it will boot wo
> > problems, or two cpus w ht. But booting with ht + two cpu's gives me the
> > other problem.
>
> Sounds like the BIOS is not rerouting the interrupts correctly. Check for
> a BIOS update.
>

I'll see if there is a new BIOS update.

/Bjorn