RX IRQs triggering for network traffic processing in multiqueue-enabled virtual machines

This document (000021267) is provided subject to the disclaimer at the end of this document.


SUSE Linux Enterprise Server 15
SUSE Linux Enterprise Server 12 Service Pack 5


  • Setup a QEMU/KVM environment [1];
  • Install openvswitch supporting dpdk (>= 2.14.2);
  • On openvswitch, configure a bridge including two dpdkvhostuserclient interfaces as described in [2], enabling multiqueue support on them;
  • Configure two SLES VMs, each one having a vNIC attached to the bridge described above and setup with multiple queues in a virtio-net / vhostuser configuration [3];
Performing massive traffic testing across the VMs and monitoring the RX IRQs being triggered within the VMs themselves using the /proc/interrupts contents, only a few of the RX IRQs associated to each virtio-net NIC were seen to be incremented.


The number of RX IRQs being triggered is related to the number of Poll Mod Drivers (PMDs) being run by Openvswitch.
Their configuration can be shown by running the command :

ovs-appctl dpif-netdev/pmd-rxq-show

To fine tune them, the pmd-cpu-mask configuration parameter is available, which specifies the CPU mask for setting the CPU affinity of the PMD threads.

The value is specified in hexadecimal (hex) format: when not specified, only one PMD thread is created per each NUMA node and, by default, pinned to any available CPU on the NUMA node.

For example, the following command assigns CPUs 2, 5, and 8 to PMDs handling:

ovs-vsctl set Open_vSwitch . other_config:pmd-cpu-mask=" 0x124"

The wider the bitmask, the more CPUs dedicated to PMDs, the more distinct RX IRQs can be triggered in the VMs.

Moreover, it is worth explicitly remarking that the RX queues being assigned to non-dedicated PMDs will not be polled.

Additional Information


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  • Document ID:000021267
  • Creation Date: 07-Nov-2023
  • Modified Date:07-Nov-2023
    • SUSE Linux Enterprise Server

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