From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751627AbYITGB1 (ORCPT ); Sat, 20 Sep 2008 02:01:27 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1750802AbYITGBS (ORCPT ); Sat, 20 Sep 2008 02:01:18 -0400 Received: from mx2.mail.elte.hu ([157.181.151.9]:42614 "EHLO mx2.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750722AbYITGBS (ORCPT ); Sat, 20 Sep 2008 02:01:18 -0400 Date: Sat, 20 Sep 2008 08:00:59 +0200 From: Ingo Molnar To: FUJITA Tomonori Cc: joerg.roedel@amd.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH] remove fullflush and nofullflush in IOMMU generic option Message-ID: <20080920060059.GA25713@elte.hu> References: <20080920012322R.fujita.tomonori@lab.ntt.co.jp> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20080920012322R.fujita.tomonori@lab.ntt.co.jp> User-Agent: Mutt/1.5.18 (2008-05-17) X-ELTE-VirusStatus: clean X-ELTE-SpamScore: -1.5 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-1.5 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.2.3 -1.5 BAYES_00 BODY: Bayesian 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 * FUJITA Tomonori wrote: > This patch against tip/x86/iommu virtually reverts > 2842e5bf3115193f05dc9dac20f940e7abf44c1a. But just reverting the > commit breaks AMD IOMMU so this patch also includes some fixes. > > The above commit adds new two options to x86 IOMMU generic kernel boot > options, fullflush and nofullflush. But such change that affects all > the IOMMUs needs more discussion (all IOMMU parties need the chance to > discuss it): > > http://lkml.org/lkml/2008/9/19/106 > > For me, adding these boot parameters doesn't make sense. > > All the hardware IOMMUs could use 'fullflush' for lazy IOTLB flushing > but Calgary doesn't support it. Intel VT-d has the different option > for it (and we can't rename it). [...] Well if the new option is desired, you dont have to rename the old option - just alias it to the new too and deprecate the old one eventually. Boot options are not really ABIs in the traditional sense anyway. But, in general, it's pretty pointless to add boot options for anything but debugging - nobody will use them unless there's a _problem_ with the default. So the right approach is to not add boot options and to make sure that the defaults are sane and intelligent. So could we work towards removing unnecessary boot options please? _If_ we want any strategy switch then that should be runtime anyway - nobody sane will reboot a server just to tune it slightly, and no distro will litter the boot commandline with hardware dependent tunings either. So it's only the default that matters, plus boot parameters for debugging. Ingo