Re: Schedule for OpenPOWER/Xen meeting

[Olivier Lambert <lambert.olivier@xxxxxxxxx>]

Thanks everyone for participating in the meeting!

Here is a recap on topics that was discussed (some partial/draft notes
from me and Damien at Vates, sorry if some are not entirely accurate):

* Page table implementation, hardware page walking, virtual memory in Xen
  * Multiple implementation, first a hashed tree structure, then later
a radix tree, closer to x86 and Linux usage.
  * Multiple page size support: 1G, 2M, 64k, 4k
  * All IO are memory mapped access

* Power arch hardware control and power management
  * Based on firmware called
[OPAL](https://open-power.github.io/skiboot/doc/opal-spec.html), Open
Power Abstraction Layer

* Interrupts are different than x86
  * Exceptions are considered interrupts in Power
  * Interrupts coming from external hardware are called external interrupts
    - On 
[KVM](https://www.kernel.org/doc/html/latest/virt/kvm/devices/xive.html)
    - On [Qemu](https://www.qemu.org/docs/master/specs/ppc-spapr-xive.html)

* There is an existing hypervisor spec on Power
  * What kind of hypercalls are needed to run a Linux guest on Power?
  * This spec need to be implemented on Xen to be the most compatible possible

* Might be interesting to join the OpenPOWER Foundation

* Toolchain to use to develop on Power
  * LLVM/CLang or GCC crosscompiler
  * Qemu emulation of Power architecture? Functional enough to begin
working on it?

* Availability of test hardware
  * Adapting the current CI loop for new architectures

* PCIe root complex each have their own IOMMU
  * Might be able to be disabled
  * Has an integrated error handling scheme

* Hardware information given by a device tree

This is all for our notes. Feel free to share if you have more content
or things to fix.


IMHO, it was very interesting, and also bringing good news:
1. There's an hypervisor specification for POWER, which will be
**really** useful if we want to implement Xen ("just" follow the spec)
2. POWER design and virt mechanisms seem -at first glance-
surprisingly similar to the Xen way (equivalent of grant table
principle etc.), and maybe it will be a great fit in the end!

There's still some technical docs to be published on the OpenPOWER
side, but they are willing to move forward relatively quickly.

In conclusion, I would say we are on the right track, and we might
have good surprises on how Xen can fit easily on POWER. Next steps?
Should we have a Xen meeting dedicated to that topic or should we wait
for the next monthly community call? We could use that time to decide
a kind of agenda for the next month and prepare some tasks to be done.

Thanks again!

Olivier.

For reference, here are the links we had during the meeting:
* https://openpowerfoundation.org/?resource_lib=power-isa-version-3-022:13
OPAL, is a combination of multiple parts22:31
* https://open-power.github.io/skiboot/doc/opal-spec.html#what-is-opal22:33
* https://github.com/open-power/docs22:34
* 
https://openpowerfoundation.org/?resource_lib=linux-on-power-architecture-reference-a-papr-linux-subset-review-draft22:37
* https://www.kernel.org/doc/html/latest/virt/kvm/devices/xive.html22:51
* https://www.qemu.org/docs/master/specs/ppc-spapr-xive.html


Le mer. 18 nov. 2020 à 16:17, Olivier Lambert
<lambert.olivier@xxxxxxxxx> a écrit :
>
> Hi!
>
> So I managed to get an agenda with basic questions. The meeting is at the 
> planned time (Nov the 19th, at 3PM central time, which is 9PM in UK and 10PM 
> in Europe).
>
> Meeting place will be: https://ibm.webex.com/meet/mendy
>
> Don't forget to ping your colleagues/friends that aren't watching this 
> mailing list actively, so they won't miss the meeting :)
>
> See you tomorrow!
>
> Olivier.
>
> Le jeu. 12 nov. 2020 à 21:44, Olivier Lambert <lambert.olivier@xxxxxxxxx> a 
> écrit :
>>
>> Okay so before having the meeting webex/whatever link, I think it would be 
>> more efficient to plan a kind of agenda, something we can pass to the 
>> OpenPOWER team in the next few days. This way, they could have some answers 
>> ready, allowing us to explore more things interactively during the meeting.
>>
>> Feel free to participate in this thread (even if you won't be at the 
>> meeting!), so we can gather and then organize a bit of what we'd like to 
>> know/discuss during this meeting.
>>
>> So go ahead and start to throw questions :)
>>
>>
>> Thanks,
>>
>> OIivier.
>>
>>
>> Le jeu. 12 nov. 2020 à 09:26, Olivier Lambert <lambert.olivier@xxxxxxxxx> a 
>> écrit :
>>>
>>> Thanks to everyone who participated in the poll. Due to the limited number 
>>> of answers, I think it's wiser to go for the second option (Thursday the 
>>> 19th), because everyone who already answered seems available that day. I'll 
>>> confirm that to OpenPOWER. When it's confirmed, I'll do a recap here 
>>> ideally with the meeting place.
>>>
>>> Thanks,
>>>
>>> Olivier.
>>>
>>>
>>> Le mar. 10 nov. 2020 à 13:41, Olivier Lambert <lambert.olivier@xxxxxxxxx> a 
>>> écrit :
>>>>
>>>> Hi everyone,
>>>>
>>>> We got 2 potential dates for the initial tech meeting with at least one 
>>>> OpenPOWER expert, so we can discuss the effort needed to port Xen on this 
>>>> architecture.
>>>>
>>>> Because of time zones (on OpenPower side, there's one guy in Australia), 
>>>> we got 2 possible schedules in November:
>>>>
>>>> 1. 3pm CT on this Thursday the 12th (! this week)
>>>> 2. Or next week Thursday the 19th
>>>>
>>>> I made a doodle-like so everyone can vote on their preferred schedule: 
>>>> https://framadate.org/QQu5rYEOEYr4ZHc4
>>>>
>>>> Note: 3pm CT would mean 9pm UTC, 10pm UTC+1 (CET). But correct me if I'm 
>>>> wrong.
>>>>
>>>> Reminder: the Cryptpad of the last Xen Community meeting contains the list 
>>>> of people interested. If you are aware of someone interested that could 
>>>> miss this email on this devel list, feel free to forward it. Cryptpad 
>>>> link: https://cryptpad.fr/pad/#/2/pad/edit/k-0Aj+Sxb5SliLWrFRBwx49V/
>>>>
>>>> Thank you and see you soon!
>>>>
>>>> Olivier.