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

[Julien Grall <julien.grall@xxxxxxx>]

Hi,

On 20/09/2016 12:27, George Dunlap wrote:
> On Tue, Sep 20, 2016 at 11:03 AM, Peng Fan <van.freenix@xxxxxxxxx> 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

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