Re: [Xen-devel] Odroid XU3 support

[Suriyan Ramasami <suriyan.r@xxxxxxxxx>]

Hello Julien,

    Thank you for the advice. I do have a follow up question.

On Thu, Apr 28, 2016 at 2:50 AM, Julien Grall <julien.grall@xxxxxxx> wrote:

Hello,

On 27/04/16 23:53, Suriyan Ramasami wrote:

        How can I check which core is currently active?
        Judging by this link on big.LITTLE architecture:
        http://forum.odroid.com/viewtopic.php?f=65&t=2580

        result of: cat /proc/cpuinfo | grep "CPU part" is
        CPU part    : 0xc07

        which stands for A7.

If you do this in dom0, it will show all of them to be 0xc07. They are
vCPUs after all.

Which is not a good idea. This means that Linux is not able to detect potential errata for the underlying cores (in this case the cortex-A15). Also some userspace may do some runtime optimization based on the kind of CPUs available in the guest.

Xen is not ready for big.LITTLE, so I would highly recommend you to disable either all the Cortex-A15 or Cortex-A7.

 

Ian did recommend that if they were in their own cpu pools it would avoid mixing them in a guest. I was researching that angle. What is your take on that?

If Linux is not recognizing it, that is a dom0/domU issue, is it not? 

Nonetheless, to start with, to add support, I think there would be less resistance if the boot cluster (a7) cpus are enabled and the other cluster disabled (a15)

For your information, I am planning to send a patch to park any CPUs whose MIDR is not matching the boot CPU one.

Regards,

--
Julien Grall

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