A script to balance IRQs for the Belkin RT3200 running OpenWRT

balance-irqs.sh

#!/bin/sh

# Function to set IRQ affinity
set_affinity() {
    irq=$1
    cpu_mask=$2

    # Check if the CPU mask is valid
    if echo "$cpu_mask" | grep -qE '^[0-9A-Fa-f]+$'; then
        echo "$cpu_mask" > "/proc/irq/$irq/smp_affinity" 2>/dev/null
        if [ $? -eq 0 ]; then
            logger "Set IRQ $irq affinity to CPU mask $cpu_mask"
        else
            logger "Failed to set IRQ $irq affinity: IO error"
        fi
    else
        logger "Invalid CPU mask for IRQ $irq: $cpu_mask"
    fi
}

# Count the number of available CPUs by reading from /proc/cpuinfo
num_cpus=$(grep -c '^processor' /proc/cpuinfo)

# List of IRQs to exclude
excluded_irqs="10 14 67 116 130 133 134 135 136 137 140"

# Iterate over /proc/interrupts to determine IRQs
while read -r line; do
    # Match lines with IRQ numbers (excluding "IPI" and "Err" lines)
    if echo "$line" | grep -E '^[[:space:]]*[0-9]+:' > /dev/null; then
        irq=$(echo "$line" | awk -F: '{print $1}' | tr -d ' ')
        device_name=$(echo "$line" | awk -F: '{print $2}' | tr -d ' ')

        # Check if the IRQ is in the excluded list
        if echo "$excluded_irqs" | grep -q "\b$irq\b"; then
            logger "Skipping excluded IRQ $irq"
            continue
        fi

        # Check if the current IRQ belongs to mt7615e
        if echo "$device_name" | grep -q "mt7615e"; then
            set_affinity "$irq" "2"  # Set IRQ for mt7615e to CPU mask 2 (cpu1)
            continue
        fi

        # Rotate IRQ affinities between available CPUs
        affinity_cpu=$((non_excluded_count % num_cpus))

        # Set the CPU mask (convert CPU number to hexadecimal bitmask)
        cpu_mask=$(printf "%X" $((1 << affinity_cpu)))

        # Apply the affinity setting
        set_affinity "$irq" "$cpu_mask"

        # Increment the non-excluded IRQ counter
        non_excluded_count=$((non_excluded_count + 1))
    fi
done < /proc/interrupts

logger "IRQ affinities have been updated."