HyperThreading CPU's

Dan Rue drue at therub.org
Mon Mar 15 12:48:31 PST 2004

HyperThreading was enabled by default as of 4.9-release

from /usr/src/UPDATING:

        FreeBSD 4.9-RELEASE.
        Support for HyperThread logical CPUs has now been enabled by
        default.  As a result, the HTT kernel option no longer exists.
        Instead, the logical CPUs are always started so that they can
        handle interrupts.  However, the extra logical CPUs are prevented
        from executing user processes by default.  To enable the logical
        CPUs, change the value of the machdep.hlt_logical_cpus from 1 to
        0.  This value can also be set from the loader as a tunable of
        the same name.


On Mon, Mar 15, 2004 at 03:38:10PM -0500, Marius M. Rex MARIUS wrote:
> In my fairly recent version of the UPDATING file for 4.9-stable it states
> that I have to use sysctl to modify the value of 'machdep.hlt_logical_cpus' to
> '0' to get all of my logical CPU's enabled under hyperthreading.
> Is this change still necessary?  sysctl spits that oid out as unknown
> when I try to look at it. I do have similar oids but nothing that matches that
> value precisely:
> machdep.cpu_idle_hlt: 1
> machdep.smp_cpus: 2
> machdep.hlt_cpus: 0
> Basically I have one CPU that is recognized as 2 CPUs by the kernel.  I
> know that works as it appears in my dmesg.  I just want to know if there
> is anything else I need to do to make sure both logical CPUs are available
> for use.
> -Marius M. Rex
> System Admin
> Community Connect Inc.
> marius at mail.communityconnect.com
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