Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756564AbZIDDkU (ORCPT ); Thu, 3 Sep 2009 23:40:20 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755512AbZIDDkT (ORCPT ); Thu, 3 Sep 2009 23:40:19 -0400 Received: from terminus.zytor.com ([198.137.202.10]:47036 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755390AbZIDDkT (ORCPT ); Thu, 3 Sep 2009 23:40:19 -0400 Message-ID: <4AA08B09.50503@zytor.com> Date: Thu, 03 Sep 2009 20:35:37 -0700 From: "H. Peter Anvin" User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1b3pre) Gecko/20090513 Fedora/3.0-2.3.beta2.fc11 Thunderbird/3.0b2 MIME-Version: 1.0 To: Tejun Heo CC: Jeremy Fitzhardinge , mingo@redhat.com, linux-kernel@vger.kernel.org, jeremy.fitzhardinge@citrix.com, stable@kernel.org, tglx@linutronix.de, mingo@elte.hu, linux-tip-commits@vger.kernel.org Subject: Re: [tip:x86/asm] x86/i386: Make sure stack-protector segment base is cache aligned References: <4AA01893.6000507@goop.org> <4AA02687.9080406@zytor.com> <4AA02B02.7080101@goop.org> <4AA031DE.2070109@zytor.com> <4AA080A0.7010804@kernel.org> <4AA08283.5020306@kernel.org> In-Reply-To: <4AA08283.5020306@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1007 Lines: 25 On 09/03/2009 07:59 PM, Tejun Heo wrote: > > Another question. Other than saving and loading an extra segment > register on kernel entry/exit, whether using the same or different > segment registers doesn't look like would make difference > performance-wise. If I'm interpreting the wording in the optimization > manual correctly, it means that each non-zero segment based memory > access will be costly regardless of which specific segment register is > in use and there's no way we can merge segment based dereferences for > stackprotector and percpu variables. > It's correct that it doesn't make any difference for access, only for load. -hpa -- H. Peter Anvin, Intel Open Source Technology Center I work for Intel. I don't speak on their behalf. -- 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/