netdev - [PATCH 6/9] sched/topology: Introduce sched_numa_hop

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Date:   Fri, 20 Jan 2023 20:24:33 -0800
From:   Yury Norov <yury.norov@...il.com>
To:     linux-kernel@...r.kernel.org,
        "David S. Miller" <davem@...emloft.net>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Barry Song <baohua@...nel.org>,
        Ben Segall <bsegall@...gle.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Gal Pressman <gal@...dia.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Haniel Bristot de Oliveira <bristot@...hat.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Ingo Molnar <mingo@...hat.com>,
        Jacob Keller <jacob.e.keller@...el.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Jason Gunthorpe <jgg@...dia.com>,
        Jesse Brandeburg <jesse.brandeburg@...el.com>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Leon Romanovsky <leonro@...dia.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Mel Gorman <mgorman@...e.de>,
        Peter Lafreniere <peter@...jl.ca>,
        Peter Zijlstra <peterz@...radead.org>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Saeed Mahameed <saeedm@...dia.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Tariq Toukan <tariqt@...dia.com>,
        Tariq Toukan <ttoukan.linux@...il.com>,
        Tony Luck <tony.luck@...el.com>,
        Valentin Schneider <vschneid@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>
Cc:     Yury Norov <yury.norov@...il.com>, linux-crypto@...r.kernel.org,
        netdev@...r.kernel.org, linux-rdma@...r.kernel.org
Subject: [PATCH 6/9] sched/topology: Introduce sched_numa_hop_mask()

From: Valentin Schneider <vschneid@...hat.com>

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@...hat.com>
Reviewed-by: Yury Norov <yury.norov@...il.com>
Signed-off-by: Yury Norov <yury.norov@...il.com>
---
 include/linux/topology.h |  7 +++++++
 kernel/sched/topology.c  | 33 +++++++++++++++++++++++++++++++++
 2 files changed, 40 insertions(+)

diff --git a/include/linux/topology.h b/include/linux/topology.h
index 72f264575698..344c2362755a 100644
--- a/include/linux/topology.h
+++ b/include/linux/topology.h
@@ -247,11 +247,18 @@ static inline const struct cpumask *cpu_cpu_mask(int cpu)
 
 #ifdef CONFIG_NUMA
 int sched_numa_find_nth_cpu(const struct cpumask *cpus, int cpu, int node);
+extern const struct cpumask *sched_numa_hop_mask(unsigned int node, unsigned int hops);
 #else
 static __always_inline int sched_numa_find_nth_cpu(const struct cpumask *cpus, int cpu, int node)
 {
 	return cpumask_nth(cpu, cpus);
 }
+
+static inline const struct cpumask *
+sched_numa_hop_mask(unsigned int node, unsigned int hops)
+{
+	return ERR_PTR(-EOPNOTSUPP);
+}
 #endif	/* CONFIG_NUMA */
 
 #endif /* _LINUX_TOPOLOGY_H */
diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
index 2bf89186a10f..1233affc106c 100644
--- a/kernel/sched/topology.c
+++ b/kernel/sched/topology.c
@@ -2124,6 +2124,39 @@ int sched_numa_find_nth_cpu(const struct cpumask *cpus, int cpu, int node)
 	return ret;
 }
 EXPORT_SYMBOL_GPL(sched_numa_find_nth_cpu);
+
+/**
+ * sched_numa_hop_mask() - Get the cpumask of CPUs at most @hops hops away from
+ *                         @node
+ * @node: The node to count hops from.
+ * @hops: Include CPUs up to that many hops away. 0 means local node.
+ *
+ * Return: On success, a pointer to a cpumask of CPUs at most @hops away from
+ * @node, an error value otherwise.
+ *
+ * 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).
+ */
+const struct cpumask *sched_numa_hop_mask(unsigned int node, unsigned int hops)
+{
+	struct cpumask ***masks;
+
+	if (node >= nr_node_ids || hops >= sched_domains_numa_levels)
+		return ERR_PTR(-EINVAL);
+
+	masks = rcu_dereference(sched_domains_numa_masks);
+	if (!masks)
+		return ERR_PTR(-EBUSY);
+
+	return masks[hops][node];
+}
+EXPORT_SYMBOL_GPL(sched_numa_hop_mask);
+
 #endif /* CONFIG_NUMA */
 
 static int __sdt_alloc(const struct cpumask *cpu_map)
-- 
2.34.1