From: Alan Cox <alan@lxorguk.ukuu.org.uk>
To: "Nakajima, Jun" <jun.nakajima@intel.com>
Cc: Banai Zoltan <bazooka@emitel.hu>,
Kelsey Hudson <khudson@compendium.us>,
James Bourne <jbourne@mtroyal.ab.ca>,
Hugh Dickins <hugh@veritas.com>,
"Reed, Timothy A" <timothy.a.reed@lmco.com>,
linux-kernel@vger.kernel.org
Subject: RE: Hyperthreading
Date: 22 Aug 2002 00:45:34 +0100 [thread overview]
Message-ID: <1029973534.26411.258.camel@irongate.swansea.linux.org.uk> (raw)
In-Reply-To: <F2DBA543B89AD51184B600508B68D4000BA1E06E@fmsmsx103.fm.intel.com>
On Wed, 2002-08-21 at 23:56, Nakajima, Jun wrote:
> Since Pentium 4 and Xeon share the same core, you see the HT bit on Pentium
> 4 as well. The HT bit does not mean HT is enabled (you can enable/disable
> usually by the BIOS setup), but the number of the threads (i.e. logical
> CPUs) in a processor package must be 2 (via cpuid instruction) so that the
> OS can be sure that HT is enabled (see setup.c). The HT bit is just useful
> as a prerequisite for HT.
If you want to know the full HT capabilities of the processor you need
to read cpuid 1 and check ebx bits 16-23.
There has been some interesting speculation as to whether you can enable
HT by undocumented mtrrs on cpus that have "ht" but claim not to be
doing HT. Clearly the value returned is settable somewhere but I've seen
no proof yet than you can enable HT on non PIV Xeons this way.
next prev parent reply other threads:[~2002-08-21 23:40 UTC|newest]
Thread overview: 42+ messages / expand[flat|nested] mbox.gz Atom feed top
2002-08-21 22:56 Hyperthreading Nakajima, Jun
2002-08-21 23:45 ` Alan Cox [this message]
-- strict thread matches above, loose matches on Subject: below --
2003-11-25 9:44 hyperthreading Gábor Lénárt
2003-11-25 9:48 ` hyperthreading Emiliano 'AlberT' Gabrielli
2003-11-25 10:05 ` hyperthreading Gábor Lénárt
2003-11-25 10:16 ` hyperthreading Arjan van de Ven
2003-11-25 10:32 ` hyperthreading Måns Rullgård
2003-11-25 10:45 ` hyperthreading Mikael Pettersson
2003-11-29 13:29 ` hyperthreading Bill Davidsen
2003-12-01 10:53 ` hyperthreading Emiliano 'AlberT' Gabrielli
2003-11-25 10:22 ` hyperthreading Karl Pitrich
2002-08-22 12:58 Hyperthreading Nir Soffer
2002-08-22 14:30 ` Hyperthreading Hugh Dickins
2002-08-22 9:15 Hyperthreading Marc Dietrich
2002-08-22 14:06 ` Hyperthreading Hugh Dickins
2002-08-22 14:36 ` Hyperthreading Marc Dietrich
2002-08-21 11:32 Hyperthreading Reed, Timothy A
2002-08-21 13:48 ` Hyperthreading James Bourne
2002-08-21 17:33 ` Hyperthreading Hugh Dickins
2002-08-21 19:34 ` Hyperthreading James Bourne
2002-08-21 21:16 ` Hyperthreading Kelsey Hudson
2002-08-21 21:55 ` Hyperthreading Banai Zoltan
2002-08-22 8:05 ` Hyperthreading venom
2002-08-26 19:00 ` Hyperthreading Kelsey Hudson
2002-08-22 8:00 ` Hyperthreading venom
2002-08-23 7:28 ` Hyperthreading Gilad Ben-Yossef
2002-08-23 8:10 ` Hyperthreading Hugh Dickins
2002-08-23 8:27 ` Hyperthreading Alan Cox
2002-08-23 8:12 ` Hyperthreading venom
2002-04-18 1:52 Hyperthreading Holzrichter, Bruce
2002-04-17 20:34 Hyperthreading Holzrichter, Bruce
2002-04-17 22:48 ` Hyperthreading Martin J. Bligh
2002-04-18 1:21 ` Hyperthreading James Bourne
2002-04-17 20:02 SMP P4 APIC/interrupt balancing James Bourne
2002-04-17 21:10 ` Hyperthreading Martin J. Bligh
2002-04-17 20:15 ` Hyperthreading Robert Love
2002-04-17 20:23 ` Hyperthreading Dave Jones
2002-04-17 21:24 ` Hyperthreading Jeff V. Merkey
2002-04-17 20:25 ` Hyperthreading James Bourne
2002-04-17 21:26 ` Hyperthreading Jeff V. Merkey
2002-04-18 0:31 ` Hyperthreading Martin J. Bligh
2002-04-18 4:50 ` Hyperthreading Jeff V. Merkey
2002-04-17 22:12 ` Hyperthreading Alan Cox
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