genirq/affinity: Provide smarter irq spreading infrastructure

The current irq spreading infrastructure is just looking at a cpumask and
tries to spread the interrupts over the mask. Thats suboptimal as it does
not take numa nodes into account.

Change the logic so the interrupts are spread across numa nodes and inside
the nodes. If there are more cpus than vectors per node, then we set the
affinity to several cpus. If HT siblings are available we take that into
account and try to set all siblings to a single vector.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Christoph Hellwig <hch@lst.de>
Cc: axboe@fb.com
Cc: keith.busch@intel.com
Cc: agordeev@redhat.com
Cc: linux-block@vger.kernel.org
Link: http://lkml.kernel.org/r/1473862739-15032-3-git-send-email-hch@lst.de

1 files changed, 149 insertions, 0 deletions

diff --git a/kernel/irq/affinity.c b/kernel/irq/affinity.c
index 32f6cfc..7812fec 100644
--- a/kernel/irq/affinity.c
+++ b/kernel/irq/affinity.c
@@ -4,6 +4,155 @@
 #include <linux/slab.h>
 #include <linux/cpu.h>
 
+static void irq_spread_init_one(struct cpumask *irqmsk, struct cpumask *nmsk,
+				int cpus_per_vec)
+{
+	const struct cpumask *siblmsk;
+	int cpu, sibl;
+
+	for ( ; cpus_per_vec > 0; ) {
+		cpu = cpumask_first(nmsk);
+
+		/* Should not happen, but I'm too lazy to think about it */
+		if (cpu >= nr_cpu_ids)
+			return;
+
+		cpumask_clear_cpu(cpu, nmsk);
+		cpumask_set_cpu(cpu, irqmsk);
+		cpus_per_vec--;
+
+		/* If the cpu has siblings, use them first */
+		siblmsk = topology_sibling_cpumask(cpu);
+		for (sibl = -1; cpus_per_vec > 0; ) {
+			sibl = cpumask_next(sibl, siblmsk);
+			if (sibl >= nr_cpu_ids)
+				break;
+			if (!cpumask_test_and_clear_cpu(sibl, nmsk))
+				continue;
+			cpumask_set_cpu(sibl, irqmsk);
+			cpus_per_vec--;
+		}
+	}
+}
+
+static int get_nodes_in_cpumask(const struct cpumask *mask, nodemask_t *nodemsk)
+{
+	int n, nodes;
+
+	/* Calculate the number of nodes in the supplied affinity mask */
+	for (n = 0, nodes = 0; n < num_online_nodes(); n++) {
+		if (cpumask_intersects(mask, cpumask_of_node(n))) {
+			node_set(n, *nodemsk);
+			nodes++;
+		}
+	}
+	return nodes;
+}
+
+/**
+ * irq_create_affinity_masks - Create affinity masks for multiqueue spreading
+ * @affinity:		The affinity mask to spread. If NULL cpu_online_mask
+ *			is used
+ * @nvecs:		The number of vectors
+ *
+ * Returns the masks pointer or NULL if allocation failed.
+ */
+struct cpumask *irq_create_affinity_masks(const struct cpumask *affinity,
+					  int nvec)
+{
+	int n, nodes, vecs_per_node, cpus_per_vec, extra_vecs, curvec = 0;
+	nodemask_t nodemsk = NODE_MASK_NONE;
+	struct cpumask *masks;
+	cpumask_var_t nmsk;
+
+	if (!zalloc_cpumask_var(&nmsk, GFP_KERNEL))
+		return NULL;
+
+	masks = kzalloc(nvec * sizeof(*masks), GFP_KERNEL);
+	if (!masks)
+		goto out;
+
+	/* Stabilize the cpumasks */
+	get_online_cpus();
+	/* If the supplied affinity mask is NULL, use cpu online mask */
+	if (!affinity)
+		affinity = cpu_online_mask;
+
+	nodes = get_nodes_in_cpumask(affinity, &nodemsk);
+
+	/*
+	 * If the number of nodes in the mask is less than or equal the
+	 * number of vectors we just spread the vectors across the nodes.
+	 */
+	if (nvec <= nodes) {
+		for_each_node_mask(n, nodemsk) {
+			cpumask_copy(masks + curvec, cpumask_of_node(n));
+			if (++curvec == nvec)
+				break;
+		}
+		goto outonl;
+	}
+
+	/* Spread the vectors per node */
+	vecs_per_node = nvec / nodes;
+	/* Account for rounding errors */
+	extra_vecs = nvec - (nodes * vecs_per_node);
+
+	for_each_node_mask(n, nodemsk) {
+		int ncpus, v, vecs_to_assign = vecs_per_node;
+
+		/* Get the cpus on this node which are in the mask */
+		cpumask_and(nmsk, affinity, cpumask_of_node(n));
+
+		/* Calculate the number of cpus per vector */
+		ncpus = cpumask_weight(nmsk);
+
+		for (v = 0; curvec < nvec && v < vecs_to_assign; curvec++, v++) {
+			cpus_per_vec = ncpus / vecs_to_assign;
+
+			/* Account for extra vectors to compensate rounding errors */
+			if (extra_vecs) {
+				cpus_per_vec++;
+				if (!--extra_vecs)
+					vecs_per_node++;
+			}
+			irq_spread_init_one(masks + curvec, nmsk, cpus_per_vec);
+		}
+
+		if (curvec >= nvec)
+			break;
+	}
+
+outonl:
+	put_online_cpus();
+out:
+	free_cpumask_var(nmsk);
+	return masks;
+}
+
+/**
+ * irq_calc_affinity_vectors - Calculate to optimal number of vectors for a given affinity mask
+ * @affinity:		The affinity mask to spread. If NULL cpu_online_mask
+ *			is used
+ * @maxvec:		The maximum number of vectors available
+ */
+int irq_calc_affinity_vectors(const struct cpumask *affinity, int maxvec)
+{
+	int cpus, ret;
+
+	/* Stabilize the cpumasks */
+	get_online_cpus();
+	/* If the supplied affinity mask is NULL, use cpu online mask */
+	if (!affinity)
+		affinity = cpu_online_mask;
+
+	cpus = cpumask_weight(affinity);
+	ret = (cpus < maxvec) ? cpus : maxvec;
+
+	put_online_cpus();
+	return ret;
+}
+
 static int get_first_sibling(unsigned int cpu)
 {
 	unsigned int ret;