Xen ARM community call - meeting minutes and date for the next one

[Julien Grall <julien.grall@arm.com>]

Hi all,

Apologies for the late sending, you will find at the end of the e-mail a
summary of the discussion from the previous call. Feel free to reply if I
missed some parts.

I suggest to have the next call on the 5th April at 5PM UTC. Any opinions?

Also do you have any specific topic you would like to talk during this call?

Cheers,

== Attendees ==

Apologies if I misspelled any name.

Stefano, Aporeto
Julien, ARM
Oleksandr, EPAM
Artem, EPAM
Thanasis, OnApp
Volodymir, EPAM

== Xen on ARM status ==

Over 100 patches in-flight for Xen on ARM:
    - PV protocols: Some are already accepted
    - NUMA support
    - GICv3 ITS support
    - Exposing and emulating a PL011 for guest
    - guest SMC forwarding for Xilinx platform
    - Interrupt latency improvement

== PV protocols ==

* PV protocols written by Stefano was merged after 10 months

Stefano: PV protocols review are moving faster
Attendees agreed

* Audio protocol: close to be accepted
* Display protocol: minor issue, a bit more design is required

Hopefully both will be ready for Xen 4.9

Oleksandr: What to do when the backend die?

(I cannot find any notes on it some I am not sure if we answered the question
during the call. I suspect it has been asked to bring up the subject on the ML).

== Interrupt latency ==

Stefano: Some improvement has been done but it is not possible to know whether
it is good. Do you have any specific IRQ latency requirements?

Artem: There is no hard latency requirements in automotive, although many
requirements depends on latency. For example:
    * Scheduling
    * GPU (implementation is sentive to interrupt latency)

Automotive is using a set of benchmark to find the virtualization overhead. This
should be low.

ACTION: Artem to send a list of benchmark

== SMC/HVC handling in Xen ==

Artem: Please review the proposal on the mailing list. See:

https://lists.xenproject.org/archives/html/xen-devel/2017-03/msg00430.html

== Deprivilege mode ==

EPAM are working on adding support for OP-TEE in Xen to allow multiple guest
access the trusted firmware.

During the discussion on the design, it was suggested to move the SMC handling
in a separate domain. This was tested using the VM event API and Mini-OS
(upstream with Chen Baozi's series to support ARM64). The first results
shows it is 10 times slower than handling SMC calls directly in the hypervisor.

Volodymir is working on another approach to deprivilege the execution by
implementing a Xen EL0.

== big.LITTLE support ==

Thanasis: Document discussed on the ML. Xen will split CPUs at boot time
(big vs little). A series will be sent on the on the ML soon.

-- 
Julien Grall

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