Regarding core disable in FreeBSD 9

[Dan Nelson]

In the last episode (Apr 13), Florian Smeets said:
> On 13.04.12 19:34, Alexander Best wrote:
> > On Sat Apr 14 12, Mahesh Babu wrote:
> >> How to disable a particular core in FreeBSD 9?  How to enable it again?
> >
> > i don't think it's possible to do that in freebsd. what you can do is to
> > disable SMP oder hyperthreading.  alternatively you can assign a certain
> > process to a certain core.
> >
> > i think there's a project to disable and enable specific cores on the
> > fly.  freebsd is pretty far behind regarding this feature.  beos was
> > able to do this anno 1998 or so afair.
> 
> You can set the following in /boot/loader.conf
> 
> hint.lapic.128.disabled=1
> hint.lapic.130.disabled=1
> 
> Where 128 and 130 are IDs of cores you want to disable, you can find the
> IDs for your CPUs/cores in
> 
> dmesg or /var/log/messages e.g.
> 
>   cpu0 (BSP): APIC ID:  0
>   cpu1 (AP): APIC ID:  2
>   cpu2 (AP): APIC ID:  4
>   cpu3 (AP): APIC ID: 16
> 
> Enabling and disabling on the fly is not possible.

You can't completely disable a core, but you can tell the scheduler not to
use it, via the cpuset command.  For example, "cpuset -s 1 -l 0,1" will
change the mask for cpuset 1 (the default set) to only allow cpus 0 and 1. 

-- 
	Dan Nelson
	dnelson at allantgroup.com