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Re: [Xen-devel] Odroid XU3 support

On 08/05/2016 12:59, Peng Fan wrote:
Hi Julien,

Hello Peng,

On Thu, Apr 28, 2016 at 10:50:33AM +0100, Julien Grall wrote:

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:

        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.

For Cortex A53 + A72 or A53 + A57, xen also not ready?

Xen is not ready at all for big.LITTLE, no matter the combinations of the CPUs.

Some of the cores you mentioned (especially A53 and A57) may contain errata that requires workaround in the Linux kernel to avoid potential data corruption or deadlock. As the vPIDR will always be equal to the boot CPU vMIDR, Linux won't apply the necessary workaround to itself.

So using big and little cores at the same time with Xen is not safe at all, even if you create CPU pool with current version of Xen.

If need to let xen support A53 + A72 or A53 + A57, what work may need to be 

I gave some insights later this thread. See:



Julien Grall

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