From mboxrd@z Thu Jan 1 00:00:00 1970 From: ykzhao Subject: Re: [RFC] - Mapping ACPI tables as CACHED Date: Fri, 23 Jul 2010 22:26:05 +0800 Message-ID: <1279895165.13929.61.camel@localhost.localdomain> References: <20100722152220.GA18290@sgi.com> <1279849573.13929.28.camel@localhost.localdomain> <20100723072301.GC23461@elte.hu> Mime-Version: 1.0 Content-Type: text/plain Content-Transfer-Encoding: 7bit Return-path: Received: from mga11.intel.com ([192.55.52.93]:37686 "EHLO mga11.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1760146Ab0GWO3v (ORCPT ); Fri, 23 Jul 2010 10:29:51 -0400 In-Reply-To: <20100723072301.GC23461@elte.hu> Sender: linux-acpi-owner@vger.kernel.org List-Id: linux-acpi@vger.kernel.org To: Ingo Molnar Cc: Jack Steiner , "tglx@linutronix.de" , "lenb@kernel.org" , "linux-acpi@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "H. Peter Anvin" , Linus Torvalds On Fri, 2010-07-23 at 15:23 +0800, Ingo Molnar wrote: > * ykzhao wrote: > > > From the above description maybe the E820_ACPI region can be mapped as > > cached. But this still depends on the BIOS. If the some shared data resides > > in the E820_ACPI region on some BIOS, maybe we can't map the E820_ACPI > > region as cached again. > > I dont think we can do this safely unless some other OS (Windows) does it as > well. (the reason is that if some BIOS messes this up then it will cause nasty > bugs/problems only on Linux.) > Yes. We can't map the corresponding ACPI region as cached under the following case: >No E820_ACPI region is reported by BIOS. In such case the ACPI table resides in the NVS region But if the BIOS can follow the spec and report the separated E820_ACPI/E820_NVS region, maybe we can give a try to map the E820_ACPI region as cached type. For example: the server machine.(The spec describes the E820_ACPI region as reclaimed memory, which means that it can be managed by OS after ACPI table is loaded). Can we add a boot option to control whether the E820_ACPI region can be mapped as cached type? > But the benefits of caching are very clear and well measured by Jack, so we > want the feature. What we can do is to add an exception for 'known good' hw > vendors - i.e. something quite close to Jack's RFC patch, but implemented a > bit more cleanly: > > Exposing x86_platform and e820 details to generic ACPI code isnt particularly > clean - there should be an ACPI accessor function for that or so: a new > acpi_table_can_be_cached(table) function or so. Agree. The function of acpi_os_map_memory will also be used on IA64 platform. It seems more reasonable to use a wrapper function to check whether the corresponding region can be mapped as cached type. > > In fact since __acpi_map_table(addr,size) is defined by architectures already, > this could be done purely within x86 code. > > Thanks, > > Ingo