On Mon, Mar 04, 2019 at 08:59:52PM +0100, Laurent Vivier wrote:
> This happens because initially powerpc code computes
> sched_domains_numa_masks of offline nodes as if they were merged with
> node 0 (because firmware doesn't provide the distance information for
> memoryless/cpuless nodes):
>
> node 0 1 2 3
> 0: 10 40 10 10
> 1: 40 10 40 40
> 2: 10 40 10 10
> 3: 10 40 10 10
*groan*... what does it do for things like percpu memory? ISTR the
per-cpu chunks are all allocated early too. Having them all use memory
out of node-0 would seem sub-optimal.
> We should have:
>
> node 0 1 2 3
> 0: 10 40 40 40
> 1: 40 10 40 40
> 2: 40 40 10 40
> 3: 40 40 40 10
Can it happen that it introduces a new distance in the table? One that
hasn't been seen before? This example only has 10 and 40, but suppose
the new node lands at distance 20 (or 80); can such a thing happen?
If not; why not?
> diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
> index 3f35ba1d8fde..24831b86533b 100644
> --- a/kernel/sched/topology.c
> +++ b/kernel/sched/topology.c
> @@ -1622,8 +1622,10 @@ void sched_init_numa(void)
> return;
>
> sched_domains_numa_masks[i][j] = mask;
> + if (!node_state(j, N_ONLINE))
> + continue;
>
> - for_each_node(k) {
> + for_each_online_node(k) {
> if (node_distance(j, k) >
> sched_domains_numa_distance[i])
> continue;
>
So you're relying on sched_domain_numa_masks_set/clear() to fix this up,
but that in turn relies on the sched_domain_numa_levels thing to stay
accurate.
This all seems very fragile and unfortunate.
