How can I disable hyperthreads, but NOT smp ?

Jason Usher jusher71 at
Tue Sep 20 20:46:58 UTC 2011

FreeBSD 6.4-RELEASE system with two physical CPUs, each of which are HT capable.  From dmesg:

cpu0 (BSP): APIC ID: 0
cpu1 (AP): APIC ID: 1
cpu2 (AP): APIC ID: 6
cpu3 (AP): APIC ID: 7

I also see this:

machdep.hyperthreading_allowed: 0

The problem is, I have reason to believe that my workload benefits greatly from SMP, but is not playing nicely with hyperthreading.  That is, it is trying to farm out 4 things at a time to a cpu setup that really is only able to do two things at a time.

How can I disable HT completely, but still retain ALL the benefits of SMP ?


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