Re: [Xen-devel] [RFC PATCH v1 00/21] ARM: Add Xen NUMA support

[Vijay Kilari <vijay.kilari@xxxxxxxxx>]

Hi Konrad,

On Fri, Feb 10, 2017 at 11:00 PM, Konrad Rzeszutek Wilk
<konrad.wilk@xxxxxxxxxx> wrote:
> On Thu, Feb 09, 2017 at 09:26:52PM +0530, vijay.kilari@xxxxxxxxx wrote:
>> From: Vijaya Kumar K <Vijaya.Kumar@xxxxxxxxxx>
>>
>> With this RFC patch series, NUMA support is added for arm platform.
>> Both DT and ACPI based NUMA support is added.
>> Only Xen is made aware of NUMA platform. Dom0 is awareness is not
>> added.
>>
>> As part of this series, the code under x86 architecture is
>> reused by moving into common files.
>> New files xen/common/numa.c and xen/commom/srat.c files are
>> added which are common for both x86 and arm.
>>
>> Patches 1 - 12 & 20 are for DT NUMA and 13 - 19 & 21 are for
>> ACPI NUMA.
>>
>> DT NUMA: The following major changes are performed
>>  - Dropped numa-node-id information from Dom0 DT.
>>    So that Dom0 devices make allocation from node 0 for
>>    devmalloc requests.
>>  - Memory DT is not deleted by EFI. It is exposed to Xen
>>    to extract numa information.
>>  - On NUMA failure, Fallback to Non-NUMA booting.
>>    Assuming all the memory and CPU's are under node 0.
>>  - CONFIG_NUMA is introduced.
>>
>> ACPI NUMA:
>>  - MADT is parsed before parsing SRAT table to extract
>>    CPU_ID to MPIDR mapping info. In Linux, while parsing SRAT
>>    table, MADT table is opened and extract MPIDR. However this
>>    approach is not working on Xen it allows only one table to
>>    be open at a time because when ACPI table is opened, Xen
>>    maps to single region. So opening ACPI tables recursively
>>    leads to overwriting of contents.
>
> Huh? Why can't you use vmap APIs to map them?
I see acpi_os_map_memory() could be used.

However, this approach of caching of cpu to MPIDR mapping by parsing MADT
before processing SRAT is much efficient.
In linux for every CPU_ID entry in SRAT read, the MADT is opened and searched
for CPU_ID to MPIDR mapping and closed. So MADT is searched n*n times.

Regards
Vijay

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