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Date:      Wed, 13 Aug 2003 18:54:26 -0600
From:      "David R. Colyer" <davedillinger@wyoming.com>
To:        freebsd-current@freebsd.org
Subject:   Re: Dual P4 2.4Ghz Xeon With Hyperthreading enabled...
Message-ID:  <200308131854.26943.davedillinger@wyoming.com>
In-Reply-To: <XFMail.20030813125214.jhb@FreeBSD.org>
References:  <XFMail.20030813125214.jhb@FreeBSD.org>

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No doubt this has been answered before, but I have an asus p4pe with a 3.06 
p4.  Naturally, it is enabled in the bios.  To enable hyperthreading do I 
need to recompile my kernel with smp support, and if so...does this apply to 
freebsd 5.1 release as well?  (my friend wants to know).  Additionally does 
changing the machdep.cpu_idle_hlt to zero make it faster?  Thanks in advance.

David R. Colyer


On Wednesday 13 August 2003 10:52 am, John Baldwin wrote:
> On 13-Aug-2003 Dr. Richard E. Hawkins wrote:
> > On Wed, Aug 13, 2003 at 11:35:14AM -0400, John Baldwin wrote:
> >> On 13-Aug-2003 Dr. Richard E. Hawkins wrote:
> >> > On Tue, Aug 12, 2003 at 08:33:57PM -0500, Cagle, John (ISS-Houston) 
wrote:
> >> >> I think the valid settings are only 0 or 1, with the default being 1
> >> >> which will disable all logical CPUs.  If you want to enable the extra
> >> >> logical CPUS, then set it to 0 (zero).  They will come online
> >> >> immediately.
> >> >
> >> > That can't be right.  I've never done anything to configure the
> >> > logical cpus on mine; they just showed up unexpectedly when i switched
> >> > from stable to current.  Now I have:
> >> >
> >> > slytherin ttyp1:hawk>sysctl -a |  grep cpu
> >> > kern.threads.virtual_cpu: 4
> >> > kern.ccpu: 1948
> >> > kern.smp.cpus: 4
> >> > hw.ncpu: 4
> >> > machdep.cpu_idle_hlt: 1
> >> > machdep.hlt_cpus: 10
> >> > machdep.hlt_logical_cpus: 1
> >> > machdep.logical_cpus_mask: 10
> >> >
> >> > It launches four logical cpus all on it's own.  It did panic during
> >> > shutdown yesterday; If I read the messages right as it flashed by, it
> >> > was because cpu#2 got the shutdown order.
> >>
> >> Your logical CPU's aren't doing anything though, even though they are
> >> started up.  John's explanation is correct.
> >
> > I've also got the report in dmesg,
> >
> > SMP: AP CPU #1 Launched!
> > SMP: AP CPU #2 Launched!
> > SMP: AP CPU #3 Launched!
> >
> >
> > Doesn't this mean that they *are* active?
>
> No, it means the kernel has started them up.  CPU's whose bits are set
> in machdep.hlt_cpus don't execute any user tasks.  Instead, they just
> sit in a loop executing the 'hlt' instruction doing nothing but servicing
> interrupts.



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