Re: [RFC 11/12] rpmsg: increase buffer size and reduce buffer number

Mathieu Poirier
2020-06-04T19:58:43Z

Hi Guennadi,

On Fri, May 29, 2020 at 09:37:21AM +0200, Guennadi Liakhovetski wrote:
> It is hard to imagine use-cases where 512 buffers would really be
> needed, whereas 512 bytes per buffer might be too little. Change this
> to use 16 16KiB buffers instead.
>
> Signed-off-by: Guennadi Liakhovetski <guennadi.liakhovetski@linux.intel.com>
> ---
> include/linux/virtio_rpmsg.h | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/virtio_rpmsg.h b/include/linux/virtio_rpmsg.h
> index 679be8b..1add468 100644
> --- a/include/linux/virtio_rpmsg.h
> +++ b/include/linux/virtio_rpmsg.h
> @@ -72,8 +72,8 @@ enum rpmsg_ns_flags {
> * can change this without changing anything in the firmware of the remote
> * processor.
> */
> -#define MAX_RPMSG_NUM_BUFS 512
> -#define MAX_RPMSG_BUF_SIZE 512
> +#define MAX_RPMSG_NUM_BUFS (512 / 32)
> +#define MAX_RPMSG_BUF_SIZE (512 * 32)

These have been a standard in the rpmsg protocol since the inception of the
subsystem 9 years ago and can't be changed without serious impact to existing
implementations.

I suggest to dynamically set the number and size of the buffers to use
based on the value of virtio_device_id::device. To do that please spin
off a new function, something like rpmsg_get_buffer_size(), and in there use
the device ID to fetch the numbers based on vdev->id->device. That way the
rpmsg driver can be used by multiple clients and the specifics of the buffers
adjusted without impact to other users.

Thanks,
Mathieu

>
> /* Address 53 is reserved for advertising remote services */
> #define RPMSG_NS_ADDR 53
> --
> 1.9.3
>