[PATCH] block: build default queue map via irq_create_affinity_masks

[Ming Lei <ming.lei@redhat.com>]

The default queue mapping builder of blk_mq_map_queues doesn't take NUMA
topo into account, so the built mapping is pretty bad, since CPUs
belonging to different NUMA node are assigned to same queue. It is
observed that IOPS drops by ~30% when running two jobs on same hctx
of null_blk from two CPUs belonging to two NUMA nodes compared with
from same NUMA node.

Address the issue by reusing irq_create_affinity_masks() for building
the default queue mapping, so that we can re-use the mapping created
for managed irq.

Lots of drivers may benefit from the change, such as nvme pci poll,
nvme tcp, ...

Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
 block/blk-mq-cpumap.c | 60 +++++++++----------------------------------
 1 file changed, 12 insertions(+), 48 deletions(-)

diff --git a/block/blk-mq-cpumap.c b/block/blk-mq-cpumap.c
index 3db84d3197f1..946e373296a3 100644
--- a/block/blk-mq-cpumap.c
+++ b/block/blk-mq-cpumap.c
@@ -10,67 +10,31 @@
 #include <linux/mm.h>
 #include <linux/smp.h>
 #include <linux/cpu.h>
+#include <linux/interrupt.h>
 
 #include <linux/blk-mq.h>
 #include "blk.h"
 #include "blk-mq.h"
 
-static int queue_index(struct blk_mq_queue_map *qmap,
-		       unsigned int nr_queues, const int q)
-{
-	return qmap->queue_offset + (q % nr_queues);
-}
-
-static int get_first_sibling(unsigned int cpu)
-{
-	unsigned int ret;
-
-	ret = cpumask_first(topology_sibling_cpumask(cpu));
-	if (ret < nr_cpu_ids)
-		return ret;
-
-	return cpu;
-}
-
 int blk_mq_map_queues(struct blk_mq_queue_map *qmap)
 {
+	struct irq_affinity_desc *masks = NULL;
+	struct irq_affinity affd = {0};
 	unsigned int *map = qmap->mq_map;
 	unsigned int nr_queues = qmap->nr_queues;
-	unsigned int cpu, first_sibling, q = 0;
+	unsigned int q;
 
-	for_each_possible_cpu(cpu)
-		map[cpu] = -1;
+	masks = irq_create_affinity_masks(nr_queues, &affd);
+	if (!masks)
+		return -ENOMEM;
 
-	/*
-	 * Spread queues among present CPUs first for minimizing
-	 * count of dead queues which are mapped by all un-present CPUs
-	 */
-	for_each_present_cpu(cpu) {
-		if (q >= nr_queues)
-			break;
-		map[cpu] = queue_index(qmap, nr_queues, q++);
-	}
+	for (q = 0; q < nr_queues; q++) {
+		unsigned int cpu;
 
-	for_each_possible_cpu(cpu) {
-		if (map[cpu] != -1)
-			continue;
-		/*
-		 * First do sequential mapping between CPUs and queues.
-		 * In case we still have CPUs to map, and we have some number of
-		 * threads per cores then map sibling threads to the same queue
-		 * for performance optimizations.
-		 */
-		if (q < nr_queues) {
-			map[cpu] = queue_index(qmap, nr_queues, q++);
-		} else {
-			first_sibling = get_first_sibling(cpu);
-			if (first_sibling == cpu)
-				map[cpu] = queue_index(qmap, nr_queues, q++);
-			else
-				map[cpu] = map[first_sibling];
-		}
+		for_each_cpu(cpu, &masks[q].mask)
+			map[cpu] = q;
 	}
-
+	kfree(masks);
 	return 0;
 }
 EXPORT_SYMBOL_GPL(blk_mq_map_queues);
-- 
2.31.1