On 09/08/22 17:04, Tariq Toukan wrote:

On 8/9/2022 3:52 PM, Valentin Schneider wrote:

quoted

On 09/08/22 13:18, Tariq Toukan wrote:

quoted

On 8/9/2022 1:02 PM, Valentin Schneider wrote:

quoted

Are there cases where we can't figure this out in advance? From what I grok
out of the two callsites you patched, all vectors will be used unless some
error happens, so compressing the CPUs in a single cpumask seemed
sufficient.

All vectors will be initialized to support the maximum number of traffic
rings. However, the actual number of traffic rings can be controlled and
set to a lower number N_actual < N. In this case, we'll be using only
N_actual instances and we want them to be the first/closest.

Ok, that makes sense, thank you.

In that case I wonder if we'd want a public-facing iterator for
sched_domains_numa_masks[%i][node], rather than copy a portion of
it. Something like the below (naming and implementation haven't been
thought about too much).

   const struct cpumask *sched_numa_level_mask(int node, int level)
   {
           struct cpumask ***masks = rcu_dereference(sched_domains_numa_masks);

           if (node >= nr_node_ids || level >= sched_domains_numa_levels)
                   return NULL;

           if (!masks)
                   return NULL;

           return masks[level][node];
   }
   EXPORT_SYMBOL_GPL(sched_numa_level_mask);

The above can be kept static, and expose only the foo() function below,
similar to my sched_cpus_set_spread().

So what I was thinking with this was to only have to export the
sched_numa_level_mask() thing and the iterator, and then consumers would be
free to use whatever storage form they want (cpumask, array, list...).

Right now I believe sched_domains_numa_masks has the right shape for the
interface (for a given node, you a cpumask per distance level) and I
don't want to impose an interface that uses just an array, but perhaps I'm
being silly and the array isn't so bad and simpler to use - that said we
could always build an array-based helper on top of the array of cpumasks
thing.

Clearly I need to scratch my head a bit longer :-)

LGTM.
How do you suggest to proceed?
You want to formalize it? Or should I take it from here?

I need to have a think (feel free to ponder and share your thoughts as
well) - I'm happy to push something if I get a brain-wave, but don't let
that hold you back either.