Hi,

The virtio spec generated from this repository https://github.com/oasis-tcs/virtio-spec includes a section dedicated to shared memory regions, described as "an additional facility available to devices that need a region of memory that’s continuously shared between the device and the driver, rather than passed between them in the way virtqueue elements are".

This version of the spec does not seem to have been released yet, although some time ago there was an attempt to use shared memory regions with virtio-fs (https://lwn.net/Articles/774495/).

Regards,
Dan

On 10/29/20 1:55 AM, Stefano Stabellini wrote:

[Please note this e-mail is from an EXTERNAL e-mail address]

Hi Alex, Arnd, Jean-Philippe, and all,

During the OpenAMP App-services call this week WindRiver gave a couple
of extremely interesting presentations, see attached slides.

Dan Milea discussed the usage of virtio between heterogeneous clusters,
i.e. virtio frontends on the Cortex-R cluster and virtio backends on
the Cortex-A cluster. They used a setup based on pre-shared memory to
make it work, which I believe is similar to the swiotlb approach we
discussed in Stratos. They noted that the last version of the virtio
spec on github had something in regards to virtio and pre-shared memory
regions that might help us cover this use-case from a spec perspective.

Dan, would you be able to share a pointer to it for clarity? So far, we
acted on the assumption that the virtio spec doesn't allow for this
architecture today; it would be fantastic if it turns out that it
already does.


The other very interesting presentation by Joshua Pincus was about
virtio-mmio and MSIs. They did excellent measurements on the
performance of virtio-mmio and they found out that the single source of
notifications (one interrupt) is the bottleneck. Adding MSIs vastly
improved performance. You can see the detailed breakdown on slide #8 of
"OpenAMP Virt I/O MMIO w/ MSI". This analysis really points in the
direction of adding MSIs to virtio-mmio.

Cheers,

Stefano




---------- Forwarded message ----------
Date: Wed, 28 Oct 2020 18:41:09 +0000
From: Nathalie Chan King Choy via App-services
    <app-services@lists.openampproject.org>
Reply-To: Nathalie Chan King Choy <nathalie@xilinx.com>
To: "app-services@lists.openampproject.org"
    <app-services@lists.openampproject.org>
Subject: [App-services] 2020-10-27 OpenAMP App-services call recording, notes,
    slides, and action items


Hi all,



The notes from yesterday’s OpenAMP App-services call can be found at:

https://github.com/OpenAMP/open-amp/wiki/OpenAMP-Application-Services-Subgroup-Meeting-Notes-2020#20201027



The link to the Webex recording is in the notes.  I am not sure how long before the recordings expire or I will hit my storage limit, so if
you need to catch up by watching the recording, please download it in the next couple weeks.



Please find attached the slides from Dan & Josh.



Action items:

* Dan & Josh to send slides (DONE)

* Stefano to start a thread w/ the folks who are working on shared memory & VirtIO



Best regards,

Nathalie C. Chan King Choy

Program Manager focused on Open Source and Community