From mboxrd@z Thu Jan 1 00:00:00 1970 Received: with ECARTIS (v1.0.0; list linux-mips); Tue, 04 Mar 2014 18:01:34 +0100 (CET) Received: from localhost.localdomain ([127.0.0.1]:55757 "EHLO linux-mips.org" rhost-flags-OK-OK-OK-FAIL) by eddie.linux-mips.org with ESMTP id S6818703AbaCDRBbGeEz2 (ORCPT ); Tue, 4 Mar 2014 18:01:31 +0100 Received: from scotty.linux-mips.net (localhost.localdomain [127.0.0.1]) by scotty.linux-mips.net (8.14.7/8.14.4) with ESMTP id s24H1Sam029696; Tue, 4 Mar 2014 18:01:28 +0100 Received: (from ralf@localhost) by scotty.linux-mips.net (8.14.7/8.14.7/Submit) id s24H1RPb029695; Tue, 4 Mar 2014 18:01:27 +0100 Date: Tue, 4 Mar 2014 18:01:27 +0100 From: Ralf Baechle To: Paul Burton Cc: Markos Chandras , linux-mips@linux-mips.org Subject: Re: [PATCH 3/5] MIPS: Set page size to 16KB for malta SMP defconfigs Message-ID: <20140304170127.GR13415@linux-mips.org> References: <1392904828-12969-1-git-send-email-markos.chandras@imgtec.com> <1392904828-12969-4-git-send-email-markos.chandras@imgtec.com> <20140221173829.GI19285@linux-mips.org> <53148C5A.7020101@imgtec.com> <20140303142921.GF13880@pburton-linux.le.imgtec.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140303142921.GF13880@pburton-linux.le.imgtec.org> User-Agent: Mutt/1.5.21 (2010-09-15) Return-Path: X-Envelope-To: <"|/home/ecartis/ecartis -s linux-mips"> (uid 0) X-Orcpt: rfc822;linux-mips@linux-mips.org Original-Recipient: rfc822;linux-mips@linux-mips.org X-archive-position: 39406 X-ecartis-version: Ecartis v1.0.0 Sender: linux-mips-bounce@linux-mips.org Errors-to: linux-mips-bounce@linux-mips.org X-original-sender: ralf@linux-mips.org Precedence: bulk List-help: List-unsubscribe: List-software: Ecartis version 1.0.0 List-Id: linux-mips X-List-ID: linux-mips List-subscribe: List-owner: List-post: List-archive: X-list: linux-mips On Mon, Mar 03, 2014 at 02:29:21PM +0000, Paul Burton wrote: > On Mon, Mar 03, 2014 at 02:06:18PM +0000, Markos Chandras wrote: > > On 02/21/2014 05:38 PM, Ralf Baechle wrote: > > >On Thu, Feb 20, 2014 at 02:00:26PM +0000, Markos Chandras wrote: > > > > > >>From: Paul Burton > > >> > > >>For Malta defconfigs which may run on an SMP configuration without > > >>hardware cache anti-aliasing, a 16KB page size is a safer default. > > >>Most notably at the moment it will avoid cache aliasing issues for > > >>multicore proAptiv systems. > > > > > >You're aware that this may cause binary compatibility issues with old > > >userland? So far the defaults were chosen to maximise compatibility > > >over performance. > > > > > > Ralf > > > > > Hi Ralf, > > > > Are you referring to programs hard coding the page size to 4k instead of > > using the getpagesize()? Well yes this could be a problem. But is that a > > real problem? We are changing the default value so whoever has such an old > > userland can easily switch to the 4k page size. It may also be a good > > opportunity to expose such application and get the fixed properly :) But if > > that's not acceptable, we can drop the patch. Paul what do you think? > > > > -- > > markos > > I think the potential backwards compatibility issue is probably not a > huge issue for Malta, but that it would make sense to dig deeper into > why proAptiv SMP systems don't run correctly with 4KB pages. You don't > actually have to look very far to find userland which depends upon 4KB > pages (*cough* android *cough*). I consider this patch an acceptable > workaround for the proAptiv problem on Malta, but I don't know enough > at the moment to say whether there's a proper fix. The issue I was refering to is that certain older binutils are creating ELF segments of insufficient alignment for large page sizes to work. Hardcoded page size is another problem - one should think that after iterating through every power of two starting with like 512 bytes programmers have sprung a clue. Ralf