[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 <dwag...@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