Messages in this thread |  | | | Subject | Re: [RFC] - Mapping ACPI tables as CACHED | | From | ykzhao <> | | Date | Fri, 23 Jul 2010 22:26:05 +0800 |
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On Fri, 2010-07-23 at 15:23 +0800, Ingo Molnar wrote: > * ykzhao <yakui.zhao@intel.com> 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
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