1.3. Tuning the network device backlog queue to avoid packet drops

Procedure

1. Determine whether tuning the backlog queue 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  18862  0  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 table format. Each line represents a CPU core starting with core 0.

   The relevant columns are:

   • First column: The total number of received frames
   • Second column: The number of dropped frames because of a full backlog queue
   • Last column: The CPU core number

2. If the values in the second column of the /proc/net/softnet_stat file increment over time, increase the size of the backlog queue:

   1. Display the current backlog queue size:

      # sysctl net.core.netdev_max_backlog
      net.core.netdev_max_backlog = 1000

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

      net.core.netdev_max_backlog = 2000

      Set the net.core.netdev_max_backlog parameter to a double of the current value.

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

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