Date: Wed, 12 Jan 2005 12:36:47 +0200 From: Giorgos Keramidas <keramida@ceid.upatras.gr> To: Timothy Luoma <lists@tntluoma.com> Cc: freebsd-questions@freebsd.org Subject: Re: Hyperthreading hurts 5.3? Message-ID: <20050112103647.GA967@orion.daedalusnetworks.priv> In-Reply-To: <B8CC38DE-6455-11D9-87A5-000D93AD26C8@tntluoma.com> References: <9094-SnapperMsgD246FC56BE0A255B@68.243.126.247> <20050112014359.GA3722@gothmog.gr> <B8CC38DE-6455-11D9-87A5-000D93AD26C8@tntluoma.com>
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On 2005-01-11 23:52, Timothy Luoma <lists@tntluoma.com> wrote:
>On Jan 11, 2005, at 8:43 PM, Giorgos Keramidas wrote:
>>On 2005-01-11 19:52, "Timothy J. Luoma" <lists@tntluoma.com> wrote:
>>>
>>> summary: should I disable hypertheading in the BIOS when running 5.3?
>>> [...]
>>> If YES, I wasn't clear if people meant "disable in BIOS" or just some
>>> configuration setting in a *.conf file.
>>
>> FWIW, that should be enough, as far as FreeBSD is concerned.
>
> sorry to be dense, but which should be enough, BIOS or conf file?
Oh, sorry about that. I must have beel sleepy when I replied and missed
that there were two questions there. I meant that disabling HT from the
BIOS setup should be enough for FreeBSD too.
> is the default to use or not use hyperthreading in the kernel/conf?
AFAICT from reading /usr/src/sys/i386/i386/mp_machdep.c, hyper-threading
support is always enabled in FreeBSD if it is also enabled in the BIOS.
The mp_topology() function contains, among other stuff:
222 void
223 mp_topology(void)
224 {
225 struct cpu_group *group;
226 int logical_cpus;
227 int apic_id;
228 int groups;
229 int cpu;
230
231 /* Build the smp_topology map. */
232 /* Nothing to do if there is no HTT support. */
233 if ((cpu_feature & CPUID_HTT) == 0)
234 return;
235 logical_cpus = (cpu_procinfo & CPUID_HTT_CORES) >> 16;
236 if (logical_cpus <= 1)
237 return;
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