On 24 Feb 2026, at 12:59, Eelco Chaudron via dev wrote:
> This patch introduces a new API to the offload provider framework that
> allows hardware offload implementations to control hash value calculation
> for the OVS_ACTION_ATTR_HASH action.
>
> Background and Motivation
> ==========================
>
> The OVS hash action (OVS_ACTION_ATTR_HASH) is used to compute a hash value
> from packet header fields, primarily for load balancing across multiple
> paths using the select group action. The hash value is stored in the
> packet's metadata and used by subsequent actions to distribute flows
> across multiple output ports.
>
> However, hardware offload implementations may require different approaches
> to hash calculation:
>
> 1. Hardware NICs may use different hash functions or hash inputs than
> the software datapath, which can lead to inconsistent load distribution
> when mixing hardware and software paths.
>
> 2. Some hardware may support enhanced hashing mechanisms (e.g., using
> symmetric hashing for bidirectional flows or hardware-specific hash
> engines) that provide better load distribution than the default
> software implementation.
>
> Design
> ======
>
> This patch adds a new optional callback to the dpif_offload_class:
>
> bool (*netdev_get_dp_hash)(const struct dpif_offload *,
> const struct netdev *ingress_netdev,
> const struct dp_packet *,
> const struct ovs_action_hash *, uint32_t *hash);
>
> The callback is invoked during hash action execution when hardware offload
> is enabled and the original ingress port is known. It receives:
> - ingress_netdev: The original ingress port where the packet was received
> - packet: The packet to be hashed
> - hash_action: The hash action parameters including algorithm and basis
>
> If the provider implements this callback and returns true, the returned
> hash value is used. Otherwise, OVS falls back to the standard hash
> calculation.
>
> NOTE: This patch needs to be applied on top of the patch series below:
> https://patchwork.ozlabs.org/project/openvswitch/list/?series=491639
> https://patchwork.ozlabs.org/project/openvswitch/list/?series=492976
>
> Signed-off-by: Eelco Chaudron <[email protected]>
> ---
> lib/dpif-netdev.c | 102 ++++++++++++++++++++++++++++++++----
> lib/dpif-offload-dummy.c | 98 ++++++++++++++++++++++++++++++++++
> lib/dpif-offload-provider.h | 12 +++++
> lib/dpif-offload.c | 19 +++++++
> lib/dpif-offload.h | 4 ++
> lib/dpif.c | 7 ++-
> lib/odp-execute.c | 15 ++++--
> lib/odp-execute.h | 2 +-
> tests/dpif-netdev.at | 47 +++++++++++++++++
> 9 files changed, 291 insertions(+), 15 deletions(-)
>
> diff --git a/lib/dpif-netdev.c b/lib/dpif-netdev.c
> index 9384edcd96..c185031045 100644
> --- a/lib/dpif-netdev.c
> +++ b/lib/dpif-netdev.c
> @@ -8514,7 +8514,28 @@ dp_execute_lb_output_action(struct
> dp_netdev_pmd_thread *pmd,
> }
> }
>
> -static void
> +static inline bool
> +dp_hw_offload_hash(struct dp_netdev_pmd_thread *pmd,
> + const struct ovs_action_hash *hash_act,
> + struct dp_packet *packet, odp_port_t *cached_in_odpp,
> + struct netdev *cached_in_netdev)
Guess I forgot use ** cached_in_netdev() here. Will send a v2...
[...]
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