Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756888Ab1E3MPw (ORCPT ); Mon, 30 May 2011 08:15:52 -0400 Received: from mx2.mail.elte.hu ([157.181.151.9]:56767 "EHLO mx2.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752885Ab1E3MPv (ORCPT ); Mon, 30 May 2011 08:15:51 -0400 Date: Mon, 30 May 2011 14:15:32 +0200 From: Ingo Molnar To: Andrew Lutomirski Cc: 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 Subject: Re: [PATCH v2 08/10] x86-64: Emulate vsyscalls Message-ID: <20110530121532.GH22324@elte.hu> References: <07445623494a3d9f02581eb06326420f5f443043.1306724657.git.luto@mit.edu> <20110530074608.GD27557@elte.hu> <20110530105937.GB20133@elte.hu> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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 Content-Length: 1613 Lines: 43 * Andrew Lutomirski wrote: > On Mon, May 30, 2011 at 6:59 AM, Ingo Molnar wrote: > > > > * Andrew Lutomirski wrote: > > > >> > >> I'd advocate waiting until glibc 2.14 comes out with this change: > >> > >> http://sourceware.org/git/?p=glibc.git;a=commit;h=a8509ca540427502bd955f35296ff7b727c7a8a1 > >> > >> I want to add a warning (ratelimited to an extremely low rate) in v3 > >> whenever any of the vsyscalls get used telling users that their legacy > >> code is suffering a performance impact, but it seems like bad form to > >> tell people to build glibc from git to avoid a regression. > > > > But only statically built binaries would be impacted in practice, > > right? The number of statically built binaries that heavily rely on > > vsyscalls ought to be a very small set ... > > With current glibc even dynamic binaries take the hit on time(). Indeed, you are right, i completely forgot that again :) > With the emulation warning (coming in v3), I get (on a Fedora > 15-based VM): > > [ 0.635493] init[1] emulated legacy vsyscall time(); upgrade your > code to avoid a performance hit. ip:ffffffffff600404 sp:7fff277fe9c8 > caller:3da3e9e27d in libc.so.6[3da3e00000+192000] Ok, so we should leave the option enabled by default and distros can flip it as they upgrade/fix glibc, right? Thanks, Ingo -- 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/