Kernel forces machdep.hlt_cpus, how to change?

[Walter Hop]

Hello all,

I'm  testing  out  FreeBSD  6.0R  on  a  Dual  Xeon. I want to do some
benchmarking  of hyperthreading before I put this machine into use, so
I am trying to turn off the HLTing of logical cpu's.

A  stock SMP kernel without any options gives the following sysctl's
on this machine:

machdep.hlt_cpus: 10
machdep.hlt_logical_cpus: 0
machdep.logical_cpus_mask: 10

So  even though I have hlt_logical_cpus at 0, the kernel seems to have
decided  to HLT my cpu's 8 and 2, the 'logical' threads on each Xeon I
assume.

I've tried to get around this by setting the following:

test# cat /boot/loader.conf
machdep.hlt_cpus=0
machdep.hlt_logical_cpus=0

But still after booting I get the same result with the cpu's HLTed.

I'm  not sure if using them for user processes actually helps, but I'd
like to experiment with the setting. Any ideas how I should accomplish
this?

Cheers!
Walter Hop
Transip BV

-- 
  Transip BV | http://www.transip.nl/
  Hoogwaardige Innovatie | Aangename Zekerheid

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Re: Kernel forces machdep.hlt_cpus, how to change?

[Colin Percival]

Walter Hop wrote:
 I'm  testing  out  FreeBSD  6.0R  on  a  Dual  Xeon. I want to do some
 benchmarking  of hyperthreading before I put this machine into use, so
 I am trying to turn off the HLTing of logical cpu's.

Read FreeBSD-SA-05:09.htt :

ftp://ftp.freebsd.org/pub/FreeBSD/CERT/advisories/FreeBSD-SA-05:09.htt.asc

and then, if you don't have any local untrusted users, consider setting
machdep.hyperthreading_allowed=1 in /boot/loader.conf.

Colin Percival
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