Re: [RFC 0/5] xen/arm: support big.little SoC

[Julien Grall <julien.grall@arm.com>]

Hi,

On 20/09/2016 12:27, George Dunlap wrote:
> On Tue, Sep 20, 2016 at 11:03 AM, Peng Fan <van.freenix@gmail.com> wrote:
>> On Tue, Sep 20, 2016 at 02:54:06AM +0200, Dario Faggioli wrote:
>>> On Mon, 2016-09-19 at 17:01 -0700, Stefano Stabellini wrote:
>>>> On Tue, 20 Sep 2016, Dario Faggioli wrote:
>> I'd like to add a computing capability in xen/arm, like this:
>>
>> struct compute_capatiliby
>> {
>>    char *core_name;
>>    uint32_t rank;
>>    uint32_t cpu_partnum;
>> };
>>
>> struct compute_capatiliby cc=
>> {
>>   {"A72", 4, 0xd08},
>>   {"A57", 3, 0xxxx},
>>   {"A53", 2, 0xd03},
>>   {"A35", 1, ...},
>> }
>>
>> Then when identify cpu, we decide which cpu is big and which cpu is little
>> according to the computing rank.
>>
>> Any comments?
>
> I think we definitely need to have Xen have some kind of idea the
> order between processors, so that the user doesn't need to figure out
> which class / pool is big and which pool is LITTLE.  Whether this sort
> of enumeration is the best way to do that I'll let Julien and Stefano
> give their opinion.

I don't think an hardcoded list of processor in Xen is the right 
solution. There are many existing processors and combinations for 
big.LITTLE so it will nearly be impossible to keep updated.

I would expect the firmware table (device tree, ACPI) to provide 
relevant data for each processor and differentiate big from LITTLE core.
Note that I haven't looked at it for now. A good place to start is 
looking at how Linux does.

Regards,


-- 
Julien Grall

_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xen.org
https://lists.xen.org/xen-devel