Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932065Ab1E3MZx (ORCPT ); Mon, 30 May 2011 08:25:53 -0400 Received: from mail-pz0-f46.google.com ([209.85.210.46]:50056 "EHLO mail-pz0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756926Ab1E3MZw convert rfc822-to-8bit (ORCPT ); Mon, 30 May 2011 08:25:52 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:sender:in-reply-to:references:from:date :x-google-sender-auth:message-id:subject:to:cc:content-type :content-transfer-encoding; b=DsS1M8O9TzNYE1EB69be5XTBOp13QgG/EeKi4QPY49XIlId4OiaQqK/4gvleC6QUHJ 8LupEnE+FQcEr/nETE+O5lou6W8ZY2Qy6/shEI/U8TmSJrMfzDdppttIKWpfMrGvz3A5 D7wIu+jpx3D8ZCTjbGjz5/iYa9FNh0hBpTfq0= MIME-Version: 1.0 In-Reply-To: <20110530121532.GH22324@elte.hu> References: <07445623494a3d9f02581eb06326420f5f443043.1306724657.git.luto@mit.edu> <20110530074608.GD27557@elte.hu> <20110530105937.GB20133@elte.hu> <20110530121532.GH22324@elte.hu> From: Andrew Lutomirski Date: Mon, 30 May 2011 08:25:32 -0400 X-Google-Sender-Auth: tOYlH0amR_I1qAIunlvOc4hK7cQ Message-ID: Subject: Re: [PATCH v2 08/10] x86-64: Emulate vsyscalls To: Ingo Molnar 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 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1828 Lines: 47 On Mon, May 30, 2011 at 8:15 AM, Ingo Molnar wrote: > > * 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? Yes. But I'll make the option control just time() instead of all three. That will also reduce the size of the patch :) --Andy -- 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/