Re: [PATCH] graph: expose node context as pointers

[Jerin Jacob <jerinjacobk@gmail.com>]

On Wed, Mar 20, 2024 at 11:02 PM Robin Jarry <rjarry@redhat.com> wrote:
>
> In some cases, the node context data is used to store two pointers
> because the data is larger than the reserved 16 bytes. Having to define
> intermediate structures just to be able to cast is tedious. Add two
> pointers that take the same space than ctx.
>
> Signed-off-by: Robin Jarry <rjarry@redhat.com>
> ---
>  lib/graph/rte_graph_worker_common.h | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/lib/graph/rte_graph_worker_common.h b/lib/graph/rte_graph_worker_common.h
> index 36d864e2c14e..a7fcdf4893ea 100644
> --- a/lib/graph/rte_graph_worker_common.h
> +++ b/lib/graph/rte_graph_worker_common.h
> @@ -112,7 +112,14 @@ struct __rte_cache_aligned rte_node {
>         };
>         /* Fast path area  */
>  #define RTE_NODE_CTX_SZ 16
> -       alignas(RTE_CACHE_LINE_SIZE) uint8_t ctx[RTE_NODE_CTX_SZ]; /**< Node Context. */
> +       alignas(RTE_CACHE_LINE_SIZE) union {
> +               uint8_t ctx[RTE_NODE_CTX_SZ];
> +               /* Convenience aliases to store pointers without complex casting. */

1) Use _extension_ to not break this on windows build. See rte_mbuf.
2) Also add static assert to make sure the following struct is not
greater than RTE_NODE_CTX_SZ. To avoid accidentally adding something
in the future.


> +               struct {
> +                       void *ctx_ptr;
> +                       void *ctx_ptr2;
> +               };
> +       }; /**< Node Context. */
>         uint16_t size;          /**< Total number of objects available. */
>         uint16_t idx;           /**< Number of objects used. */
>         rte_graph_off_t off;    /**< Offset of node in the graph reel. */
> --
> 2.44.0
>