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    SubjectRe: [PATCH v4 5/7] sched/topology: Introduce sched_numa_hop_mask()
    On Fri, Sep 23, 2022 at 04:55:40PM +0100, Valentin Schneider wrote:
    > Tariq has pointed out that drivers allocating IRQ vectors would benefit
    > from having smarter NUMA-awareness - cpumask_local_spread() only knows
    > about the local node and everything outside is in the same bucket.
    >
    > sched_domains_numa_masks is pretty much what we want to hand out (a cpumask
    > of CPUs reachable within a given distance budget), introduce
    > sched_numa_hop_mask() to export those cpumasks.
    >
    > Link: http://lore.kernel.org/r/20220728191203.4055-1-tariqt@nvidia.com
    > Signed-off-by: Valentin Schneider <vschneid@redhat.com>
    > ---
    > include/linux/topology.h | 12 ++++++++++++
    > kernel/sched/topology.c | 31 +++++++++++++++++++++++++++++++
    > 2 files changed, 43 insertions(+)
    >
    > diff --git a/include/linux/topology.h b/include/linux/topology.h
    > index 4564faafd0e1..3e91ae6d0ad5 100644
    > --- a/include/linux/topology.h
    > +++ b/include/linux/topology.h
    > @@ -245,5 +245,17 @@ static inline const struct cpumask *cpu_cpu_mask(int cpu)
    > return cpumask_of_node(cpu_to_node(cpu));
    > }
    >
    > +#ifdef CONFIG_NUMA
    > +extern const struct cpumask *sched_numa_hop_mask(int node, int hops);
    > +#else
    > +static inline const struct cpumask *sched_numa_hop_mask(int node, int hops)
    > +{
    > + if (node == NUMA_NO_NODE && !hops)
    > + return cpu_online_mask;
    > +
    > + return ERR_PTR(-EOPNOTSUPP);
    > +}
    > +#endif /* CONFIG_NUMA */
    > +
    >
    > #endif /* _LINUX_TOPOLOGY_H */
    > diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
    > index 8739c2a5a54e..ee77706603c0 100644
    > --- a/kernel/sched/topology.c
    > +++ b/kernel/sched/topology.c
    > @@ -2067,6 +2067,37 @@ int sched_numa_find_closest(const struct cpumask *cpus, int cpu)
    > return found;
    > }
    >
    > +/**
    > + * sched_numa_hop_mask() - Get the cpumask of CPUs at most @hops hops away.
    > + * @node: The node to count hops from.
    > + * @hops: Include CPUs up to that many hops away. 0 means local node.
    > + *
    > + * Requires rcu_lock to be held. Returned cpumask is only valid within that
    > + * read-side section, copy it if required beyond that.
    > + *
    > + * Note that not all hops are equal in distance; see sched_init_numa() for how
    > + * distances and masks are handled.
    > + *
    > + * Also note that this is a reflection of sched_domains_numa_masks, which may change
    > + * during the lifetime of the system (offline nodes are taken out of the masks).
    > + */

    Since it's exported, can you declare function parameters and return
    values properly?

    > +const struct cpumask *sched_numa_hop_mask(int node, int hops)
    > +{
    > + struct cpumask ***masks = rcu_dereference(sched_domains_numa_masks);
    > +
    > + if (node == NUMA_NO_NODE && !hops)
    > + return cpu_online_mask;
    > +
    > + if (node >= nr_node_ids || hops >= sched_domains_numa_levels)
    > + return ERR_PTR(-EINVAL);
    > +
    > + if (!masks)
    > + return NULL;
    > +
    > + return masks[hops][node];
    > +}
    > +EXPORT_SYMBOL_GPL(sched_numa_hop_mask);
    > +
    > #endif /* CONFIG_NUMA */
    >
    > static int __sdt_alloc(const struct cpumask *cpu_map)
    > --
    > 2.31.1

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