Re: [Xen-devel] Odroid XU3 support

[Julien Grall <julien.grall@xxxxxxx>]

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

Regards,

--
Julien Grall

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