Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754072AbYCHMmL (ORCPT ); Sat, 8 Mar 2008 07:42:11 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752102AbYCHMl4 (ORCPT ); Sat, 8 Mar 2008 07:41:56 -0500 Received: from one.firstfloor.org ([213.235.205.2]:46499 "EHLO one.firstfloor.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751999AbYCHMl4 (ORCPT ); Sat, 8 Mar 2008 07:41:56 -0500 Date: Sat, 8 Mar 2008 13:43:32 +0100 From: Andi Kleen To: Willy Tarreau Cc: Andi Kleen , Chris Snook , Andrew Buehler , Frederik Deweerdt , belcampo , linux-kernel@vger.kernel.org Subject: Re: Hyperthreading performance oddities Message-ID: <20080308124332.GF27074@one.firstfloor.org> References: <47BE9781.3030304@zonnet.nl> <20080222100630.GE5906@slug> <47D14526.2070103@gmail.com> <47D192BF.5090501@redhat.com> <87zltae3y7.fsf@basil.nowhere.org> <20080308073000.GH8953@1wt.eu> <20080308114655.GB27074@one.firstfloor.org> <20080308123436.GA24982@1wt.eu> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20080308123436.GA24982@1wt.eu> User-Agent: Mutt/1.4.2.1i Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1107 Lines: 22 >On HT, I normally observe lower performance than on UP. Hmm weird. It might be interesting to investigate in detail what is going on there. > model name : Intel(R) Core(TM)2 Duo CPU E8200 @ 2.66GHz > 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 pbe nx lm constant_tsc pni monitor ds_cpl vmx smx est tm2 ssse3 cx16 xtpr lahf_lm Dual core systems generally have it, It leads to better scheduling on some older OS because in many aspects dual core is nearer HT than a true dual socket systems. There was no traditional way to express "core siblings" in CPUID so they just faked HT again, but added some additional ways to detect real dual coreness. AMD does it similar (but slightly different). Of course modern kernels don't need such hacks anymore. -Andi -- 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/