2.5. Increasing the time SoftIRQs can run on the CPU

Procedure

1. To determine whether tuning the net.core.netdev_budget parameter is needed, display the counters in the /proc/net/softnet_stat file:

   # awk '{for (i=1; i<=NF; i++) printf strtonum("0x" $i) (i==NF?"\n":" ")}' /proc/net/softnet_stat | column -t
   221951548  0  0      0  0  0  0  0  0  0  0  0  0
   192058677  0  20380  0  0  0  0  0  0  0  0  0  1
   455324886  0  0      0  0  0  0  0  0  0  0  0  2
   ...

   This awk command converts the values in /proc/net/softnet_stat from hexadecimal to decimal format and displays them in the table format. Each line represents a CPU core starting with core 0.

   The relevant columns are:

   • First column: The total number of received frames.
   • Third column: The number times softirqd processes that could not retrieve all packets from interfaces in one NAPI polling cycle.
   • Last column: The CPU core number.

2. If the counters in the third column of the /proc/net/softnet_stat file increment over time, tune the system:

   1. Display the current values of the net.core.netdev_budget_usecs and net.core.netdev_budget parameters:

      # sysctl net.core.netdev_budget_usecs net.core.netdev_budget
      net.core.netdev_budget_usecs = 2000
      net.core.netdev_budget = 300

      With these settings, softirqd processes have up to 2000 microseconds to process up to 300 messages from the NIC in one polling cycle. Polling ends based on which condition is met first.

   2. Create the /etc/sysctl.d/10-netdev_budget.conf file with the following content:

      net.core.netdev_budget = 600
      net.core.netdev_budget_usecs = 4000

      Set the parameters to a double of their current values.

   3. Load the settings from the /etc/sysctl.d/10-netdev_budget.conf file:

      # sysctl -p /etc/sysctl.d/10-netdev_budget.conf