Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Wed, 21 Aug 2002 18:52:51 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Wed, 21 Aug 2002 18:52:50 -0400 Received: from fmr05.intel.com ([134.134.136.6]:63184 "EHLO hermes.jf.intel.com") by vger.kernel.org with ESMTP id ; Wed, 21 Aug 2002 18:52:19 -0400 Message-ID: From: "Nakajima, Jun" To: Banai Zoltan , Kelsey Hudson Cc: James Bourne , Hugh Dickins , "Reed, Timothy A" , linux-kernel@vger.kernel.org Subject: RE: Hyperthreading Date: Wed, 21 Aug 2002 15:56:12 -0700 MIME-Version: 1.0 X-Mailer: Internet Mail Service (5.5.2653.19) Content-Type: text/plain; charset="iso-8859-1" Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3380 Lines: 93 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. Thanks, Jun -----Original Message----- From: Banai Zoltan [mailto:bazooka@emitel.hu] Sent: Wednesday, August 21, 2002 2:55 PM To: Kelsey Hudson Cc: James Bourne; Hugh Dickins; Reed, Timothy A; linux-kernel@vger.kernel.org Subject: Re: Hyperthreading On Wed, Aug 21, 2002 at 02:16:11PM -0700, Kelsey Hudson wrote: > On Wed, 21 Aug 2002, James Bourne wrote: > > > On Wed, 21 Aug 2002, Hugh Dickins wrote: > > > > > You do need CONFIG_SMP and a processor capable of HyperThreading, > > > i.e. Pentium 4 XEON; but CONFIG_MPENTIUM4 is not necessary for HT, > > > just appropriate to that processor in other ways. > > > > I was under the impression that the only CPU capable of hyperthreading was > > the P4 Xeon. Is this not correct? I don't know of any other CPUs that > > have the ht feature. > > This is currently correct, although I believe Intel has plans to release a > Hyperthreading-capable version of its desktop P4. If this is correct, and there is not destop P4 capable of ht, then what does mean the ht flag in cpuinfo? $cat /proc/cpuinfo processor : 0 vendor_id : GenuineIntel cpu family : 15 model : 1 model name : Intel(R) Pentium(R) 4 CPU 1.70GHz stepping : 2 cpu MHz : 1694.907 cache size : 256 KB fdiv_bug : no hlt_bug : no f00f_bug : no coma_bug : no fpu : yes fpu_exception : yes cpuid level : 2 wp : yes flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm bogomips : 3381.65 ^^ > > > Also, looking at setup.c it's hard to determine if CONFIG_SMP is > > actually required, but it doesn't look like it... > > Of course it's required. How are you to take advantage of a "second CPU" > if your scheduler only works on a uniprocessor machine? > > -- > Kelsey Hudson khudson@compendium.us > Software Engineer/UNIX Systems Administrator > Compendium Technologies, Inc (619) 725-0771 > --------------------------------------------------------------------------- > > - > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ -- Banai Zoltan - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/