Skip site navigation (1)Skip section navigation (2)
Date:      Fri, 13 Apr 2012 13:03:19 -0500
From:      Dan Nelson <dnelson@allantgroup.com>
To:        Florian Smeets <flo@freebsd.org>
Cc:        Alexander Best <arundel@freebsd.org>, Mahesh Babu <maheshbabu90@yahoo.co.in>, "freebsd-hackers@freebsd.org" <freebsd-hackers@freebsd.org>
Subject:   Re: Regarding core disable in FreeBSD 9
Message-ID:  <20120413180318.GA61234@dan.emsphone.com>
In-Reply-To: <4F8865AB.10504@FreeBSD.org>
References:  <1334333913.65753.YahooMailNeo@web193204.mail.sg3.yahoo.com> <20120413173440.GA48030@freebsd.org> <4F8865AB.10504@FreeBSD.org>

next in thread | previous in thread | raw e-mail | index | archive | help
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@allantgroup.com



Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?20120413180318.GA61234>