[Arm-dev] Gigabyte MP30-AR0

[Gordan Bobic]

On 2016-03-15 18:32, Richard W.M. Jones wrote:
> On Mon, Mar 14, 2016 at 03:00:35PM +0000, Gordan Bobic wrote:
>> On 2016-03-01 22:32, Michael Howard wrote:
>> >On 01/03/2016 22:26, Richard W.M. Jones wrote:
>> >>On Mon, Feb 29, 2016 at 03:20:03PM +0000, Michael Howard wrote:
>> >>>Just to let you know, I can't get this to work. aarch64 is supposed
>> >>>to be binary compatible, with the correct libraries installed, but
>> >>>I'm thinking the cpu isn't.
>> >>>
>> >>>All I get is 'cannot execute binary file: Exec format error',
>> >>>regardless  of what I try.
>> >>As I understand it the problem is page size - 64K was chosen by
>> >>Red Hat for aarch64, where as 4K is the norm on armv7.
>> >>
>> >>Anyway, you can run a 32 bit VM and it works well -- in fact a lot
>> >>faster than regular 32 bit armv7 hardware.
>> >>
>> >
>> >Yes, with CONFIG_ARM64_4K_PAGES=y and CONFIG_COMPAT=y, 32 bit
>> >binaries run fine.
>> 
>> I built a kernel with these options enabled, but chrooting into an
>> armv5tel subtree segfaults immediately. :-(
> 
> I may be missing some context here, but is there some reason not to
> just use a VM?

Performance for one.

> It's more predictable because you'll be running the
> same kernel that the 32 bit environment is expecting.

The aarch64 environment seems no less predictable with a
kernel defaulting to 4K pages. There are also other reasons,
for example I want to run ZFS on the host and don't want to
have to re-export the shares to guests via a network file
system.

> Also it will
> (or should) work without you needing to compile your own host kernel.

Well, as far as the host kernel is concerned:

1) I already posted a link with a selection of posts from Linus himself
explaining at some length why using large default pages is a bad idea
at the best of times (and for all other cases where bigger pages do give
us that 3% speed-up we can use hugepages directly instead).

2) The kernel that ships is deprecated and was never a LT kernel (4.2).

So switching to the next LT kernel better configured for practically
any task seems advantageous in every way.

I now have docker happily running armv5tel guests.

Gordan