Re: [Xen-devel] [SUSPECTED SPAM]Re: Xen on POWER

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 09/03/18 10:38, awokd wrote:
> On Fri, March 9, 2018 10:03 am, Andrew Cooper wrote:
>> On 09/03/2018 09:37, awokd wrote:
>> Xen currently has x86 and ARM as supported architectures, so there is a
>> reasonable split between common and arch-specific code.  As a start, you'd
>> need to implement enough of the arch stubs to make Power9 build, then work
>> on trying to get it to boot.
>>
>> As a guess, the ARM port is going to be far closer to what you're
>> looking to do than the x86 side.
> Thanks for your reply, that helps. Would it make sense to target 4.8.3
> stable to mostly avoid trying to hit a moving target, then port "up"? I'll
> investigate how ARM support was added too, that's relatively fresh and
> could be used as a model.

As Wei says, work against staging only.  There will probably be quite a
lot of rearranging involved, and it will very quickly go stale.

For reference, the ARM port took more than a year to be usable, but a
non-trivial part of that time was work to make the common and arch split
better.  How long it will actually take depends most on how much time
you've got to put towards it.

I can guess exactly why you want 4.8.3, but I wouldn't expect to have
something usable before the next release of Qubes.  As you get closer to
completion, Qubes will want to move forwards to newer Xen anyway.

>> Porting is one thing, but as you identify below, not  letting it wither
>> is very different.  I can't predict how much ongoing maintenance would be
>> required, but it certainly can't be left alone once "complete".
> Assuming it would be a similar workload to maintaining ARM, any idea if
> we're talking multiple FTEs here or just a fraction of one? Trying to get
> a sense of if it's something that could be maintained in one person's
> off-hours.

I'd expect to be fairly busy in your off-hours, but there is plenty of
Xen specific expertise available from the general and other arch
maintainers.  The main thing which is missing is anyone who is familiar
with Power9 itself.

Once the initial port is done, a lot of the effort goes towards new
features, or attempting to undo some of the corners you will inevitably
cut to get it started.

>
>> There is certainly some interest in getting Power work, and the touted
>> system benefits are clear to see, but porting Xen and maintaining the port
>> is not going to be a trivial task.  If you are up for the challenge, then
>> I think it would a great opportunity.
> Don't expect it to be easy but it sounds like a fun challenge with
> something of value at the end of the tunnel.

I expect that once the ball is rolling, it will pick up momentum, given
the interest I've already seen on IRC.  You probably want to hang out on
freenode #xendevel

~Andrew

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