Re: [RFC][PATCH 1/2] ARM64: add cpu topology definition

Hanjun Guo
2013-08-15T01:02:19Z

On 2013-8-14 19:27, Catalin Marinas wrote:
> On Mon, Jul 29, 2013 at 10:54:01AM +0100, Will Deacon wrote:
>> On Mon, Jul 29, 2013 at 10:46:06AM +0100, Vincent Guittot wrote:
>>> On 27 July 2013 12:42, Hanjun Guo <hanjun.guo@linaro.org> wrote:
>>>> Power aware scheduling needs the cpu topology information to improve the
>>>> cpu scheduler decision making.
>>>
>>> It's not only power aware scheduling. The scheduler already uses
>>> topology and cache sharing when CONFIG_SCHED_MC and/or
>>> CONFIG_SCHED_SMT are enable. So you should also add these configs for
>>> arm64 so the scheduler can use it
>>
>> ... except that the architecture doesn't define what the AFF fields in MPIDR
>> really represent. Using them to make key scheduling decisions relating to
>> cache proximity seems pretty risky to me, especially given the track record
>> we've seen already on AArch32 silicon. It's a convenient register if it
>> contains the data we want it to contain, but we need to force ourselves to
>> come to terms with reality here and simply use it as an identifier for a
>> CPU.
>>
>> Can't we just use the device-tree to represent this topological data for
>> arm64? Lorenzo has been working on bindings in this area.
>
> Catching up on email after holiday - I agree with Will here, we should
> use DT for representing the topology (or ACPI) and not rely on the MPIDR
> value.
>

Ok, I'm working on the ACPI part now, Thanks for your comments.

Regards
Hanjun