[Discussion]: Enhance virtio rpmsg bus driver buffer allocation

[Divin Raj <divin.raj@arm.com>]

On 10/23/23 11:44 AM, Divin Raj wrote:
> Hello all,
>
> I am reaching out with reference to the patch discussed here: Enhanced
> virtio rpmsg bus driver buffer allocation.
> <https://lore.kernel.org/all/CAH2Cfb-sv3SAL8bcczC-Dc3_r58MYZCS7s7zGtn1Qfo3mmBqVg@mail.gmail.com/>
>
> I've been keenly following the developments around enhancing buffer
> allocation strategies, especially those focused on dynamic buffer sizing
> and the considerations for systems under varying memory constraints.This
> work is highly relevant to several projects I am involved in, and I am
> quite interested in its progression. May I kindly request an update on
> the current phase of these initiatives? Additionally, I am eager to know
> if there would be an opportunity for me to contribute to enhancing the
> patch, possibly by working on improvements or assisting in verification
> processes.
>
> Furthermore, if there are any condensed resources, summaries, or
> specific threads that encapsulate recent advancements or discussions on
> this topic, I would be grateful to receive directions to them.
>
> I appreciate everyone's dedicated efforts and invaluable contributions
> to this area of development. Looking forward to the updates.
>
> Regards Divin
>
Hello Linux Community,

In one of our internal projects, we encountered a challenge with RPMSG
buffer allocation. Our goal is to optimize memory allocation for an
out-of-tree RPMSG Ethernet device driver using virtio. This is to ensure
support for packet sizes matching the standard MTU (Maximum Transmission
Unit) size of 1500 bytes.

To mitigate this issue, There are few possible solutions:

1. Configure buffer size and number through Kconfig.
2. Permit the firmware creator to determine the most suitable value from
   the resource table.
3. Enable independent configurations on both ends. This approach would
support both dynamic and fixed buffer configurations using a generic
allocator.

Reference:

[1]:
https://lore.kernel.org/all/1548949280-31794-4-git-send-email-xiaoxiang@xiaomi.com/
[2]: https://lore.kernel.org/all/20190701061353.GE1263@builder/


Draft Design Overview:

Based on the reference patch and the discussions, we have outlined the
following key points for the belw design:

1. Assure compatibility, enabling both Linux and the remote system to
interchangeably transmit and receive messages, irrespective of size.
2. For systems with constrained shared memory:
Systems with small, shared memory, we need to deal with a
limited/optimized memory chunk. To avoid memory fragmentation, the
allocator should have a pre-reserved buffer pool
3. The implementation should ensure that the remote side does not
receive messages based on its allocation parameters.

do you think it could make sense?

High level view:
+------------------+                               +------------------+
|                  |                               |                  |
|      Linux       |                               |      Remote      |
|                  |                               |                  |
|   +----------+   |       +-----------------+     |   +----------+   |
|   |   RPMSG  |   | <---> | Buffer Allocator|<--->|   | RPMSG    |   |
|   +----------+   |       | (Dynamic/Static)|     |   +----------+   |
|                  |       +-----------------+     |                  |
+------------------+                               +------------------+


Detailed view:

                   +-------------------------+
                   |  Message Creation       |
                   |  (Both Linux/Remote)    |
                   +------------+------------+
                                |
                                v
                   +-------------------------+
                   | Determine the allocation|
                   | strategy                |
                   +------------+------------+
                                |
                 +--------------+--------------+
                 |                             |
+-------------------------------+  +-------------------------------+
| Dynamic allocation            |  | Static allocation             |
| (Buffer allocator allocates   |  | (Pre-reserved memory          |
| memory space as needed,       |  | space)                        |
| based on the current          |  |                               |
| message requirement )         |  |                               |
+-------------------------------+  +-------------------------------+

We would greatly appreciate any feedback, suggestions, or improvements
you could provide.

Thank you for your time and consideration.

Regards
Divin
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