RE: [PATCH v2 2/2] lib/graph: default-align rte_graph_cluster_stats

[Marat Khalili <marat.khalili@huawei.com>]

> -----Original Message-----
> From: Jerin Jacob <jerinjacobk@gmail.com>
> Sent: Tuesday 17 June 2025 16:50
> 
> > > > -struct __rte_cache_aligned rte_graph_cluster_node_stats {
> > > > +struct rte_graph_cluster_node_stats {
> > >
> > > This is a fastpath structure. No need to change the alignment here.
> >
> > rte_graph_cluster_stats includes it, so unfortunately would stay cache-
> aligned regardless of the attributes unless we make
> rte_graph_cluster_node_stats default-aligned as well. If you are sure that
> we need to keep node one cache-aligned we can return to rte_malloc
> solution (or posix_memalign, but I would prefer not to hand-code aligned
> realloc).
> 
> I think, existing following code will take care of this. Are you
> seeing the sanitizer issue if the change is only updating
> rte_graph_cluster_stats alignment?

Yes, still seeing the sanitizer issue. And if fails even before reaching clusters, on the struct rte_graph_cluster_stats itself because I believe alignment propagates from members to enclosing structs.

>         /* For a given cluster, max nodes will be the max number of graphs */
>         cluster_node_size += cluster->nb_graphs * sizeof(struct rte_node *);
>         cluster_node_size = RTE_ALIGN(cluster_node_size,
> RTE_CACHE_LINE_SIZE);

Please correct me if I am wrong, AFAIU it looks like this in memory:
- rte_graph_cluster_stats
- cluster_node
  - rte_graph_cluster_node_stats
- rte_node *[nb_graphs]
- padding of rte_node pointers array to cacheline
- cluster_node
  - rte_graph_cluster_node_stats
- rte_node *[nb_graphs]...

cluster_node_size calculation above ensures correct distance between cluster_node structs due to presence of the rte_node pointers arrays in between, but alignment of the first cluster_node still depends on the alignment of rte_graph_cluster_stats, and each of the next ones depends on the previous. We could of course re-align the first one manually (in each loop, after allocating some extra space), but to me it looks like the job rte_malloc could easier do for us. What do you think would be the right way forward?