From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755508Ab1FHKfe (ORCPT ); Wed, 8 Jun 2011 06:35:34 -0400 Received: from mx2.mail.elte.hu ([157.181.151.9]:35564 "EHLO mx2.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753881Ab1FHKfc (ORCPT ); Wed, 8 Jun 2011 06:35:32 -0400 Date: Wed, 8 Jun 2011 12:35:09 +0200 From: Ingo Molnar To: Andi Kleen Cc: pageexec@freemail.hu, Andrew Lutomirski , x86@kernel.org, Thomas Gleixner , linux-kernel@vger.kernel.org, Jesper Juhl , Borislav Petkov , Linus Torvalds , Andrew Morton , Arjan van de Ven , Jan Beulich , richard -rw- weinberger , Mikael Pettersson , Brian Gerst , Louis Rilling , Valdis.Kletnieks@vt.edu Subject: Re: [PATCH v5 8/9] x86-64: Emulate legacy vsyscalls Message-ID: <20110608103509.GA13393@elte.hu> References: <20110608091120.GI27166@one.firstfloor.org> <4DEF424F.2351.1C15AD40@pageexec.freemail.hu> <20110608100612.GJ27166@one.firstfloor.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20110608100612.GJ27166@one.firstfloor.org> User-Agent: Mutt/1.5.20 (2009-08-17) X-ELTE-SpamScore: -2.0 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-2.0 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.3.1 -2.0 BAYES_00 BODY: Bayes spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Andi Kleen wrote: > > eventually may even go away as time progresses and linux systems > > begin to fully rely on the vdso instead. > > That assumes that everyone uses glibc and also updates their > userland. As pointed out many times that's a deeply flawed > assumption. No, it does not assume it: if a particular usecase cares *so* little about updates that it won't ever update their userland and kernel then they have no problem: they'll have what they had before. If they are willing to update the *kernel* then they will have to consider what every kernel update brings with itself: legacy facilities are de-emphasised all the time (while the ABI is still fully guaranteed) so user-space should not assume that newer kernels will offer the exact same performance tradeoffs as before. Nor do i think have you cited any *real* example - you are just talking hypotheticals with very little specifics. ABI does not mean 'executes the same instructions', guaranteeing that would be crazy. Thanks, Ingo