[PATCH v2 3/3] wifi: iwlwifi: pcie: optimize MSI-X interrupt affinity

[Adrian Garcia Cicuelo <adriangarciacasado42@gmail.com>]

Implement a balanced RSS queue distribution by skipping CPU0 for
high-rate MSI-X interrupts when multiple CPUs are online. This reduces
contention with system housekeeping tasks on the boot core and improves
overall throughput.

Signed-off-by: Adrian Garcia Cicuelo <adriangarciacicuelo@gmail.com>
---
 drivers/net/wireless/intel/iwlwifi/pcie/gen1_2/trans.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/drivers/net/wireless/intel/iwlwifi/pcie/gen1_2/trans.c b/drivers/net/wireless/intel/iwlwifi/pcie/gen1_2/trans.c
index 4560d92d7..87149f29e 100644
--- a/drivers/net/wireless/intel/iwlwifi/pcie/gen1_2/trans.c
+++ b/drivers/net/wireless/intel/iwlwifi/pcie/gen1_2/trans.c
@@ -1683,7 +1683,17 @@ static void iwl_pcie_irq_set_affinity(struct iwl_trans *trans,
 		 * Get the cpu prior to the place to search
 		 * (i.e. return will be > i - 1).
 		 */
+		/*
+		 * Balanced distribution: skip CPU0 for high-rate RSS queues
+		 * to avoid contention with system housekeeping.
+		 */
 		cpu = cpumask_next(i - offset, cpu_online_mask);
+		if (cpu >= nr_cpu_ids)
+			cpu = cpumask_first(cpu_online_mask);
+
+		if (cpu == 0 && num_online_cpus() > 1)
+			cpu = cpumask_next(0, cpu_online_mask);
+
 		cpumask_set_cpu(cpu, &trans_pcie->affinity_mask[i]);
 		ret = irq_set_affinity_hint(trans_pcie->msix_entries[i].vector,
 					    &trans_pcie->affinity_mask[i]);
-- 
2.47.3