[PATCH v4 8/9] blk-mq: use hk cpus only when isolcpus=managed_irq is enabled

Daniel Wagner
2024-12-19T15:57:19Z

When isolcpus=managed_irq 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=managed_irq,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 <wagi@kernel.org>
---
block/blk-mq-cpumap.c | 66 +++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 66 insertions(+)

diff --git a/block/blk-mq-cpumap.c b/block/blk-mq-cpumap.c
index b3a863c2db3231624685ab54a1810b22af4111f4..38016bf1be8af14ef368e68d3fd12416858e3da6 100644
--- a/block/blk-mq-cpumap.c
+++ b/block/blk-mq-cpumap.c
@@ -61,11 +61,74 @@ unsigned int blk_mq_num_online_queues(unsigned int max_queues)
}
EXPORT_SYMBOL_GPL(blk_mq_num_online_queues);

+/*
+ * blk_mq_map_hk_queues - Create housekeeping CPU to hardware queue mapping
+ * @qmap: CPU to hardware queue map
+ *
+ * Create a housekeeping CPU to hardware queue mapping in @qmap. If the
+ * isolcpus feature is enabled and blk_mq_map_hk_queues returns true,
+ * @qmap contains a valid configuration honoring the managed_irq
+ * configuration. If the isolcpus feature is disabled this function
+ * returns false.
+ */
+static bool blk_mq_map_hk_queues(struct blk_mq_queue_map *qmap)
+{
+ struct cpumask *hk_masks;
+ cpumask_var_t isol_mask;
+ unsigned int queue, cpu, nr_masks;
+
+ if (!housekeeping_enabled(HK_TYPE_MANAGED_IRQ))
+ return false;
+
+ /* map housekeeping cpus to matching hardware context */
+ nr_masks = qmap->nr_queues;
+ hk_masks = group_cpus_evenly(&nr_masks);
+ if (!hk_masks)
+ goto fallback;
+
+ for (queue = 0; queue < qmap->nr_queues; queue++) {
+ for_each_cpu(cpu, &hk_masks[queue % nr_masks])
+ 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_MANAGED_IRQ));
+
+ 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, nr_masks;

+ if (blk_mq_map_hk_queues(qmap))
+ return;
+
nr_masks = qmap->nr_queues;
masks = group_cpus_evenly(&nr_masks);
if (!masks) {
@@ -121,6 +184,9 @@ void blk_mq_map_hw_queues(struct blk_mq_queue_map *qmap,
if (!dev->bus->irq_get_affinity)
goto fallback;

+ if (blk_mq_map_hk_queues(qmap))
+ return;
+
for (queue = 0; queue < qmap->nr_queues; queue++) {
mask = dev->bus->irq_get_affinity(dev, queue + offset);
if (!mask)

--
2.47.1