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

Daniel Wagner
2024-08-06T12:07:45Z

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@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