Re: [Xen-devel] Odroid XU3 support

[Peng Fan <van.freenix@xxxxxxxxx>]

Hi Julien,

On Mon, May 09, 2016 at 10:49:58AM +0100, Julien Grall wrote:
>
>
>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:
>>>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.
>>
>>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 
>>done?
>
>I gave some insights later this thread. See:
>
>http://lists.xen.org/archives/html/xen-devel/2016-05/msg00466.html

Thanks for this info. Do you have plan to add bit.LITTLE support for xen?
I would like to use this on AArch64 platform-:)

Thanks,
Peng.

>
>Regards,
>
>-- 
>Julien Grall

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