From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1030843AbWKOSnF (ORCPT ); Wed, 15 Nov 2006 13:43:05 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1030836AbWKOSnF (ORCPT ); Wed, 15 Nov 2006 13:43:05 -0500 Received: from gw.goop.org ([64.81.55.164]:56984 "EHLO mail.goop.org") by vger.kernel.org with ESMTP id S1030846AbWKOSnD (ORCPT ); Wed, 15 Nov 2006 13:43:03 -0500 Message-ID: <455B5FB6.7010009@goop.org> Date: Wed, 15 Nov 2006 10:43:02 -0800 From: Jeremy Fitzhardinge User-Agent: Thunderbird 1.5.0.8 (X11/20061107) MIME-Version: 1.0 To: Ingo Molnar CC: Arjan van de Ven , akpm@osdl.org, ak@suse.de, linux-kernel@vger.kernel.org, Michael.Fetterman@cl.cam.ac.uk, Ian Campbell Subject: Re: i386 PDA patches use of %gs References: <1158046540.2992.5.camel@laptopd505.fenrus.org> <45075829.701@goop.org> <20060913095942.GA10075@elte.hu> <45082F1C.8000003@goop.org> <20061115182613.GA2227@elte.hu> <20061115182915.GA2705@elte.hu> In-Reply-To: <20061115182915.GA2705@elte.hu> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Ingo Molnar wrote: > for example, your test_fs() code does: > > for(i = 0; i < COUNT; i++) { > asm volatile("push %%fs; mov %1, %%fs; addl $1, %%fs:%0; popl %%fs" > : "+m" (*offset): "r" (seg) : "memory"); > sync(); > } > > that loads (and uses) a single selector value for %fs, and doesnt do any > mixed use as far as i can see. I'm not sure what you're getting at. Each loop iteration is analogous to a user->kernel->user transition with respect to the save/reload/use/restore pattern on the segment register. In this case, %fs starts as a null selector, gets reloaded with a non NULL selector, and then is restored to null. Do you mean some other mixing? J