Hello (anybody there?),

Is there a way to disable "Hyper-Threading Technology" in modern FreeBSD systems?

At the time of FreeBSD-SA-05:09.htt, it was suggested to use the following workaround:

setting the "machdep.hlt_logical_cpus" tunable: # echo "machdep.hlt_logical_cpus=1" >> /boot/loader.conf Use of this workaround is not recommended on "dual-core" systems, as this workaround will also disable one of the processor cores.

But this OID no longer seems to exist and I do not want to disable other processor cores.

My use case is a VirtualBox dedicated server where I believe using HTT might be problematic because: 1/ running two busy virtual machines on the same physical core could severely impact their performance 2/ the virtualizer might expose the real CPU to the virtual machines, which might in turn attempt to use HTT for themselves

Best regards,

Hubert

For example on a bi-Xeon X5650 FreeBSD 8.0p2 system, the relevant sysctl OIDs are:

kern.ccpu: 0 <cpu count="24" mask="0xffffff">0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23</cpu> <cpu count="12" mask="0xfff">0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11</cpu> <cpu count="2" mask="0x3">0, 1</cpu> <cpu count="2" mask="0xc">2, 3</cpu> <cpu count="2" mask="0x30">4, 5</cpu> <cpu count="2" mask="0xc0">6, 7</cpu> <cpu count="2" mask="0x300">8, 9</cpu> <cpu count="2" mask="0xc00">10, 11</cpu> <cpu count="12" mask="0xfff000">12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23</cpu> <cpu count="2" mask="0x3000">12, 13</cpu> <cpu count="2" mask="0xc000">14, 15</cpu> <cpu count="2" mask="0x30000">16, 17</cpu> <cpu count="2" mask="0xc0000">18, 19</cpu> <cpu count="2" mask="0x300000">20, 21</cpu> <cpu count="2" mask="0xc00000">22, 23</cpu> kern.smp.cpus: 24 debug.kdb.stop_cpus: 1 hw.ncpu: 24 machdep.hlt_cpus: 0

Perhaps by playing with the mask?