IRQ management patterns for performance optimization

Optimizing network performance with IRQ management

Different IRQ management patterns can significantly impact network performance across multiple cloud platforms and virtual machine sizes. This Learning Path presents various IRQ distribution strategies, along with scripts to implement them on your systems.

Network interrupt requests (IRQs) can be distributed across CPU cores in various ways, each with potential benefits depending on your workload characteristics and system configuration. By strategically assigning network IRQs to specific cores, you can improve cache locality, reduce contention, and potentially boost overall system performance.

The following patterns have been tested on various systems and can be implemented using the provided scripts. An optimal pattern is suggested at the conclusion of this Learning Path, but your specific workload might benefit from a different approach.

Common IRQ distribution patterns

Four main distribution strategies offer different performance characteristics:

• Default: uses the IRQ pattern provided at boot time by the Linux kernel
• Random: assigns all IRQs to cores without overlap with network IRQs
• Housekeeping: assigns all non-network IRQs to specific dedicated cores
• NIC-focused: assigns network IRQs to single or multiple ranges of cores, including pairs

Scripts to implement IRQ management patterns

The scripts below demonstrate how to implement different IRQ management patterns on your system. Each script targets a specific distribution strategy. Before running these scripts, identify your network interface name using ip link show and determine your system’s CPU topology with lscpu. Always test these changes in a non-production environment first, as improper IRQ assignment can impact system stability.

Housekeeping pattern

The housekeeping pattern isolates non-network IRQs to dedicated cores, reducing interference with your primary workloads.

Replace #core range here with your desired CPU range (for example: “0,3”):

    

        
        
HOUSEKEEP=#core range here (example: "0,3")

for irq in $(awk '/ACPI:Ged/ {sub(":","",$1); print $1}' /proc/interrupts); do
    echo $HOUSEKEEP | sudo tee /proc/irq/$irq/smp_affinity_list >/dev/null
done

    

Paired core pattern

The paired core assignment pattern distributes network IRQs across CPU core pairs for better cache coherency.

This example works for a 16 vCPU machine. Replace #interface name with your network interface (for example: “ens5”):

    

        
        
IFACE=#interface name (example: "ens5")

PAIRS=("0,1" "2,3" "4,5" "6,7" "8,9" "10,11" "12,13" "14,15")

# Match IRQs for the NIC
mapfile -t irqs < <(grep "$IFACE-Tx-Rx" /proc/interrupts | awk '{gsub(":","",$1); print $1}')

i=0
for irq in "${irqs[@]}"; do
    pair=${PAIRS[$((i % ${#PAIRS[@]}))]}
    echo "$pair" | sudo tee /proc/irq/$irq/smp_affinity_list >/dev/null
    echo "Set IRQ $irq -> CPUs $pair"
    ((i++))
done

    

Range assignment pattern

The range assignment pattern assigns network IRQs to a specific range of cores, providing dedicated network processing capacity.

Replace #interface name with your network interface (for example: “ens5”):

    

        
        
IFACE=#interface name (example: "ens5")

for irq in $(awk '/'$IFACE'/ {sub(":","",$1); print $1}' /proc/interrupts); do
    echo 0-15 | sudo tee /proc/irq/$irq/smp_affinity_list > /dev/null
done

    

Each pattern offers different performance characteristics depending on your workload. The housekeeping pattern reduces system noise, paired cores optimize cache usage, and range assignment provides dedicated network processing capacity. Improper configuration can degrade performance or stability, so always test these patterns in a non-production environment to determine which provides the best results for your specific use case.

Continue to the next section for additional guidance.