[PATCH 3/4 V3 net-next] net: mana: add a function to spread IRQs per CPUs
From: Souradeep Chakrabarti
Date: Mon Jan 29 2024 - 01:22:08 EST
From: Yury Norov <yury.norov@xxxxxxxxx>
Souradeep investigated that the driver performs faster if IRQs are
spread on CPUs with the following heuristics:
1. No more than one IRQ per CPU, if possible;
2. NUMA locality is the second priority;
3. Sibling dislocality is the last priority.
Let's consider this topology:
Node 0 1
Core 0 1 2 3
CPU 0 1 2 3 4 5 6 7
The most performant IRQ distribution based on the above topology
and heuristics may look like this:
IRQ Nodes Cores CPUs
0 1 0 0-1
1 1 1 2-3
2 1 0 0-1
3 1 1 2-3
4 2 2 4-5
5 2 3 6-7
6 2 2 4-5
7 2 3 6-7
The irq_setup() routine introduced in this patch leverages the
for_each_numa_hop_mask() iterator and assigns IRQs to sibling groups
as described above.
According to [1], for NUMA-aware but sibling-ignorant IRQ distribution
based on cpumask_local_spread() performance test results look like this:
/ntttcp -r -m 16
NTTTCP for Linux 1.4.0
---------------------------------------------------------
08:05:20 INFO: 17 threads created
08:05:28 INFO: Network activity progressing...
08:06:28 INFO: Test run completed.
08:06:28 INFO: Test cycle finished.
08:06:28 INFO: ##### Totals: #####
08:06:28 INFO: test duration :60.00 seconds
08:06:28 INFO: total bytes :630292053310
08:06:28 INFO: throughput :84.04Gbps
08:06:28 INFO: retrans segs :4
08:06:28 INFO: cpu cores :192
08:06:28 INFO: cpu speed :3799.725MHz
08:06:28 INFO: user :0.05%
08:06:28 INFO: system :1.60%
08:06:28 INFO: idle :96.41%
08:06:28 INFO: iowait :0.00%
08:06:28 INFO: softirq :1.94%
08:06:28 INFO: cycles/byte :2.50
08:06:28 INFO: cpu busy (all) :534.41%
For NUMA- and sibling-aware IRQ distribution, the same test works
15% faster:
/ntttcp -r -m 16
NTTTCP for Linux 1.4.0
---------------------------------------------------------
08:08:51 INFO: 17 threads created
08:08:56 INFO: Network activity progressing...
08:09:56 INFO: Test run completed.
08:09:56 INFO: Test cycle finished.
08:09:56 INFO: ##### Totals: #####
08:09:56 INFO: test duration :60.00 seconds
08:09:56 INFO: total bytes :741966608384
08:09:56 INFO: throughput :98.93Gbps
08:09:56 INFO: retrans segs :6
08:09:56 INFO: cpu cores :192
08:09:56 INFO: cpu speed :3799.791MHz
08:09:56 INFO: user :0.06%
08:09:56 INFO: system :1.81%
08:09:56 INFO: idle :96.18%
08:09:56 INFO: iowait :0.00%
08:09:56 INFO: softirq :1.95%
08:09:56 INFO: cycles/byte :2.25
08:09:56 INFO: cpu busy (all) :569.22%
[1] https://lore.kernel.org/all/20231211063726.GA4977@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/
Signed-off-by: Yury Norov <yury.norov@xxxxxxxxx>
Co-developed-by: Souradeep Chakrabarti <schakrabarti@xxxxxxxxxxxxxxxxxxx>
---
.../net/ethernet/microsoft/mana/gdma_main.c | 29 +++++++++++++++++++
1 file changed, 29 insertions(+)
diff --git a/drivers/net/ethernet/microsoft/mana/gdma_main.c b/drivers/net/ethernet/microsoft/mana/gdma_main.c
index d33b27214539..05a0ac054823 100644
--- a/drivers/net/ethernet/microsoft/mana/gdma_main.c
+++ b/drivers/net/ethernet/microsoft/mana/gdma_main.c
@@ -1249,6 +1249,35 @@ void mana_gd_free_res_map(struct gdma_resource *r)
r->size = 0;
}
+static __maybe_unused int irq_setup(unsigned int *irqs, unsigned int len, int node)
+{
+ const struct cpumask *next, *prev = cpu_none_mask;
+ cpumask_var_t cpus __free(free_cpumask_var);
+ int cpu, weight;
+
+ if (!alloc_cpumask_var(&cpus, GFP_KERNEL))
+ return -ENOMEM;
+
+ rcu_read_lock();
+ for_each_numa_hop_mask(next, node) {
+ weight = cpumask_weight_andnot(next, prev);
+ while (weight > 0) {
+ cpumask_andnot(cpus, next, prev);
+ for_each_cpu(cpu, cpus) {
+ if (len-- == 0)
+ goto done;
+ irq_set_affinity_and_hint(*irqs++, topology_sibling_cpumask(cpu));
+ cpumask_andnot(cpus, cpus, topology_sibling_cpumask(cpu));
+ --weight;
+ }
+ }
+ prev = next;
+ }
+done:
+ rcu_read_unlock();
+ return 0;
+}
+
static int mana_gd_setup_irqs(struct pci_dev *pdev)
{
unsigned int max_queues_per_port = num_online_cpus();
--
2.34.1