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    SubjectRe: [PATCH net-next V4 1/3] sched/topology: Add NUMA-based CPUs spread API
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    On 8/9/2022 3:52 PM, Valentin Schneider wrote:
    > On 09/08/22 13:18, Tariq Toukan wrote:
    >> On 8/9/2022 1:02 PM, Valentin Schneider wrote:
    >>>
    >>> 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().

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


    > #define for_each_numa_level_mask(node, lvl, mask) \
    > for (mask = sched_numa_level_mask(node, lvl); mask; \
    > mask = sched_numa_level_mask(node, ++lvl))
    >
    > void foo(int node, int cpus[], int ncpus)
    > {
    > const struct cpumask *mask;
    > int lvl = 0;
    > int i = 0;
    > int cpu;
    >
    > rcu_read_lock();
    > for_each_numa_level_mask(node, lvl, mask) {
    > for_each_cpu(cpu, mask) {
    > cpus[i] = cpu;
    > if (++i == ncpus)
    > goto done;
    > }
    > }
    > done:
    > rcu_read_unlock();
    > }
    >

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