From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1030810AbWKOSYX (ORCPT ); Wed, 15 Nov 2006 13:24:23 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1030811AbWKOSYX (ORCPT ); Wed, 15 Nov 2006 13:24:23 -0500 Received: from gw.goop.org ([64.81.55.164]:60293 "EHLO mail.goop.org") by vger.kernel.org with ESMTP id S1030810AbWKOSYW (ORCPT ); Wed, 15 Nov 2006 13:24:22 -0500 Message-ID: <455B5B55.20803@goop.org> Date: Wed, 15 Nov 2006 10:24:21 -0800 From: Jeremy Fitzhardinge User-Agent: Thunderbird 1.5.0.8 (X11/20061107) MIME-Version: 1.0 To: Arjan van de Ven CC: Ingo Molnar , Andi Kleen , Eric Dumazet , akpm@osdl.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] i386-pda UP optimization References: <1158046540.2992.5.camel@laptopd505.fenrus.org> <1158047806.2992.7.camel@laptopd505.fenrus.org> <200611151227.04777.dada1@cosmosbay.com> <200611151232.31937.ak@suse.de> <20061115172003.GA20403@elte.hu> <455B4E2F.7040408@goop.org> <1163613702.31358.145.camel@laptopd505.fenrus.org> In-Reply-To: <1163613702.31358.145.camel@laptopd505.fenrus.org> Content-Type: text/plain; charset=ISO-8859-15 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Arjan van de Ven wrote: > segment register accesses really are not cheap. > Also really it'll be better to use the register userspace is not using, > but we had that discussion before; could you remind me why you picked > %gs in the first place? > To leave open the possibility of using the compiler's TLS support in the kernel for percpu. I also measured the cost of reloading %gs vs %fs, and found no difference between reloading a null selector vs a non-null selector. J