Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1750772AbXACNhT (ORCPT ); Wed, 3 Jan 2007 08:37:19 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1750779AbXACNhT (ORCPT ); Wed, 3 Jan 2007 08:37:19 -0500 Received: from pentafluge.infradead.org ([213.146.154.40]:38525 "EHLO pentafluge.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750772AbXACNhR (ORCPT ); Wed, 3 Jan 2007 08:37:17 -0500 Subject: Re: kernel + gcc 4.1 = several problems From: Arjan van de Ven To: Alan Cc: Grzegorz Kulewski , Mikael Pettersson , s0348365@sms.ed.ac.uk, torvalds@osdl.org, 76306.1226@compuserve.com, akpm@osdl.org, bunk@stusta.de, greg@kroah.com, linux-kernel@vger.kernel.org, yanmin_zhang@linux.intel.com In-Reply-To: <20070103124410.4cb191dd@localhost.localdomain> References: <200701030212.l032CDXe015365@harpo.it.uu.se> <20070103102944.09e81786@localhost.localdomain> <20070103124410.4cb191dd@localhost.localdomain> Content-Type: text/plain Organization: Intel International BV Date: Wed, 03 Jan 2007 05:32:16 -0800 Message-Id: <1167831136.3095.8.camel@laptopd505.fenrus.org> Mime-Version: 1.0 X-Mailer: Evolution 2.8.2.1 (2.8.2.1-2.fc6) Content-Transfer-Encoding: 7bit X-SRS-Rewrite: SMTP reverse-path rewritten from by pentafluge.infradead.org See http://www.infradead.org/rpr.html Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1103 Lines: 26 On Wed, 2007-01-03 at 12:44 +0000, Alan wrote: > > > fixed. At that point an i686 kernel would contain i686 instructions and > > > actually run on all i686 processors ending all the i586 pain for most > > > users and distributions. > > > > Could you explain why CMOV is pointless now? Are there any benchmarks > > proving that? > > Take a look at the recent ffmpeg bits on the mplayer list for one example > I have to hand - P4 cmov is pretty slow. The crypto folks find the same > things. cmov is effectively the same cost as a compare and jump, in both cases the cpu needs to do a prediction, and on a mispredict, restart. the reason cmov can make sense is because it's smaller code... -- if you want to mail me at work (you don't), use arjan (at) linux.intel.com Test the interaction between Linux and your BIOS via http://www.linuxfirmwarekit.org - 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/