Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Mon, 5 Nov 2001 16:49:57 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Mon, 5 Nov 2001 16:49:48 -0500 Received: from postfix2-1.free.fr ([213.228.0.9]:65448 "HELO postfix2-1.free.fr") by vger.kernel.org with SMTP id convert rfc822-to-8bit; Mon, 5 Nov 2001 16:49:40 -0500 Date: Mon, 5 Nov 2001 20:04:33 +0100 (CET) From: =?ISO-8859-1?Q?G=E9rard_Roudier?= X-X-Sender: To: Josh Fryman Cc: Linus Torvalds , , Subject: Re: 2.4.14-pre6 In-Reply-To: <20011105162753.626cbdb6.fryman@cc.gatech.edu> Message-ID: <20011105195626.T2092-100000@gerard> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 5 Nov 2001, Josh Fryman wrote: > > Basically, you get two virtual CPU's per die, and each CPU can run two > > threads at the same time. It slows some stuff down, because it makes for > > much more cache pressure, but Intel claims up to 30% improvement on some > > loads that scale well. > > > > The 30% is probably a marketing number (ie it might be more like 10% on > > more normal loads), but you have to give them points for interesting > > technology <) > > Specifically, the 30% comes in two places. Using Intel proprietary > benchmarks (unreleased, according to the footnotes) they find that a > typical IA32 instruction mix uses some 35% of system resources in an > advanced device like the P4 with NetBurst. the rest is idle. > > by using the SMT model with two virtual systems - each with complete > register sets and independent APICs, sharing only the backend exec > units - they claim you get a 30% improvement in wall-clock time. This > is supposed to be on their benchmarks *without* recompiling anything. To > get "additional" improvement, using code to take advantage of the dual > virtual CPUs nature of the chip and recompiling should give some > unquantified gain. All things being equal, this probably will make a NxMHz P4 be as fast as a NxMHz PIII. But the new complexity it may require in real life may just turn the gain into just nil. What a great improvement, indeed! :-) G?rard. - 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/