[PATCH 1/3] domain_conf: Added configs for RSS and Hash report.

[Daniel P. Berrangé]

On Thu, Dec 30, 2021 at 08:01:43AM +0200, Andrew Melnychenko wrote:
> Added "rss" and "rss_hash_report" configuration that should be used with
> qemu virtio RSS.
> Both options are triswitches. Used as "driver" options and affects only NIC
> with model type "virtio".
> In other patches - options should turn on virtio-net RSS and hash properties.
> 
> Signed-off-by: Andrew Melnychenko <andrew at daynix.com>
> ---
>  docs/formatdomain.rst         | 15 +++++++++++++++
>  docs/schemas/domaincommon.rng | 10 ++++++++++
>  src/conf/domain_conf.c        | 31 ++++++++++++++++++++++++++++++-
>  src/conf/domain_conf.h        |  2 ++
>  4 files changed, 57 insertions(+), 1 deletion(-)
> 
> diff --git a/docs/formatdomain.rst b/docs/formatdomain.rst
> index d4f30bb8af..f7b784ed26 100644
> --- a/docs/formatdomain.rst
> +++ b/docs/formatdomain.rst
> @@ -5305,6 +5305,21 @@ following attributes are available for the ``"virtio"`` NIC driver:
>     only for ``vhostuser`` type. :since:`Since 3.7.0 (QEMU and KVM only)`
>     **In general you should leave this option alone, unless you are very certain
>     you know what you are doing.**
> +``rss``
> +   The ``rss`` option enables in-qemu/ebpf RSS for virtio NIC. RSS works with
> +   virtio and tap backends only. Virtio NIC will be launched with "rss"
> +   property. Qemu may load eBPF RSS if it has CAP_SYS_ADMIN permissions.

QEMU won't have CAP_SYS_ADMIN with libvirt unless someone goes out of their
way to make the libvirt host configuration insecure. We would consider such
a config to be unsupported aside from developers experimenting with stuff,
so I don't think it merits documentation.

> +   In other cases, "in-qemu" RSS is used.

So this is only realistic scenario that can be supported under
libvirt.

> +   **In general you should leave this option alone, unless you are very certain
> +   you know what you are doing.**
> +``rss_hash_report``
> +   The ``rss_hash_report`` option enables in-qemu RSS hash report for virtio
> +   NIC. Virtio NIC will be launched with "hash" property. Ebpf RSS doesn't
> +   support hash report yet. Usually enabled alongside with ``rss``.
> +   Without ``rss`` option, the hash report doesn't affect steering
> +   itself but provides vnet header with a calculated hash.
> +   **In general you should leave this option alone, unless you are very certain
> +   you know what you are doing.**
>  virtio options
>     For virtio interfaces, `Virtio-specific options <#elementsVirtio>`__ can also
>     be set. ( :since:`Since 3.5.0` )

Regards,
Daniel
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