[PATCH v3 15/15] blk-mq: use hk cpus only when isolcpus=io_queue is enabled

[Daniel Wagner]

When isolcpus=io_queue is enabled all hardware queues should run on the
housekeeping CPUs only. Thus ignore the affinity mask provided by the
driver. Also we can't use blk_mq_map_queues because it will map all CPUs
to first hctx unless, the CPU is the same as the hctx has the affinity
set to, e.g. 8 CPUs with isolcpus=io_queue,2-3,6-7 config

  queue mapping for /dev/nvme0n1
        hctx0: default 2 3 4 6 7
        hctx1: default 5
        hctx2: default 0
        hctx3: default 1

  PCI name is 00:05.0: nvme0n1
        irq 57 affinity 0-1 effective 1 is_managed:0 nvme0q0
        irq 58 affinity 4 effective 4 is_managed:1 nvme0q1
        irq 59 affinity 5 effective 5 is_managed:1 nvme0q2
        irq 60 affinity 0 effective 0 is_managed:1 nvme0q3
        irq 61 affinity 1 effective 1 is_managed:1 nvme0q4

where as with blk_mq_hk_map_queues we get

  queue mapping for /dev/nvme0n1
        hctx0: default 2 4
        hctx1: default 3 5
        hctx2: default 0 6
        hctx3: default 1 7

  PCI name is 00:05.0: nvme0n1
        irq 56 affinity 0-1 effective 1 is_managed:0 nvme0q0
        irq 61 affinity 4 effective 4 is_managed:1 nvme0q1
        irq 62 affinity 5 effective 5 is_managed:1 nvme0q2
        irq 63 affinity 0 effective 0 is_managed:1 nvme0q3
        irq 64 affinity 1 effective 1 is_managed:1 nvme0q4

Signed-off-by: Daniel Wagner <dwagner at suse.de>
---
 block/blk-mq-cpumap.c | 56 +++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 56 insertions(+)

diff --git a/block/blk-mq-cpumap.c b/block/blk-mq-cpumap.c
index c1277763aeeb..7e026c2ffa02 100644
--- a/block/blk-mq-cpumap.c
+++ b/block/blk-mq-cpumap.c
@@ -60,11 +60,64 @@ unsigned int blk_mq_num_online_queues(unsigned int max_queues)
 }
 EXPORT_SYMBOL_GPL(blk_mq_num_online_queues);
 
+static bool blk_mq_hk_map_queues(struct blk_mq_queue_map *qmap)
+{
+	struct cpumask *hk_masks;
+	cpumask_var_t isol_mask;
+
+	unsigned int queue, cpu;
+
+	if (!housekeeping_enabled(HK_TYPE_IO_QUEUE))
+		return false;
+
+	/* map housekeeping cpus to matching hardware context */
+	hk_masks = group_cpus_evenly(qmap->nr_queues);
+	if (!hk_masks)
+		goto fallback;
+
+	for (queue = 0; queue < qmap->nr_queues; queue++) {
+		for_each_cpu(cpu, &hk_masks[queue])
+			qmap->mq_map[cpu] = qmap->queue_offset + queue;
+	}
+
+	kfree(hk_masks);
+
+	/* map isolcpus to hardware context */
+	if (!alloc_cpumask_var(&isol_mask, GFP_KERNEL))
+		goto fallback;
+
+	queue = 0;
+	cpumask_andnot(isol_mask,
+		       cpu_possible_mask,
+		       housekeeping_cpumask(HK_TYPE_IO_QUEUE));
+
+	for_each_cpu(cpu, isol_mask) {
+		qmap->mq_map[cpu] = qmap->queue_offset + queue;
+		queue = (queue + 1) % qmap->nr_queues;
+	}
+
+	free_cpumask_var(isol_mask);
+
+	return true;
+
+fallback:
+	/* map all cpus to hardware context ignoring any affinity */
+	queue = 0;
+	for_each_possible_cpu(cpu) {
+		qmap->mq_map[cpu] = qmap->queue_offset + queue;
+		queue = (queue + 1) % qmap->nr_queues;
+	}
+	return true;
+}
+
 void blk_mq_map_queues(struct blk_mq_queue_map *qmap)
 {
 	const struct cpumask *masks;
 	unsigned int queue, cpu;
 
+	if (blk_mq_hk_map_queues(qmap))
+		return;
+
 	masks = group_cpus_evenly(qmap->nr_queues);
 	if (!masks) {
 		for_each_possible_cpu(cpu)
@@ -118,6 +171,9 @@ void blk_mq_dev_map_queues(struct blk_mq_queue_map *qmap,
 	const struct cpumask *mask;
 	unsigned int queue, cpu;
 
+	if (blk_mq_hk_map_queues(qmap))
+		return;
+
 	for (queue = 0; queue < qmap->nr_queues; queue++) {
 		mask = get_queue_affinity(dev_data, dev_off, queue);
 		if (!mask)

-- 
2.46.0