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Network Packet Processing Statistics

This page describes how to get information about network packet processing statistics inside network stack.

Network stack contains infrastructure to figure out how long the network packet processing takes either in sending or receiving path. There are two Kconfig options that control this. For transmit (TX) path the option is called CONFIG_NET_PKT_TXTIME_STATS and for receive (RX) path the options is called CONFIG_NET_PKT_RXTIME_STATS. Note that for TX, all kind of network packet statistics is collected. For RX, only UDP, TCP or raw packet type network packet statistics is collected.

After enabling these options, the net stats network shell command will show this information:

Avg TX net_pkt (11484) time 67 us
Avg RX net_pkt (11474) time 43 us

Note

The values above and below are from emulated qemu_x86 board and UDP traffic

The TX time tells how long it took for network packet from its creation to when it was sent to the network. The RX time tells the time from its creation to when it was passed to the application. The values are in microseconds. The statistics will be collected per traffic class if there are more than one transmit or receive queues defined in the system. These are controlled by CONFIG_NET_TC_TX_COUNT and CONFIG_NET_TC_RX_COUNT options.

If you enable CONFIG_NET_PKT_TXTIME_STATS_DETAIL or CONFIG_NET_PKT_RXTIME_STATS_DETAIL options, then additional information for TX or RX network packets are collected when the network packet traverses the IP stack.

After enabling these options, the net stats will show this information:

Avg TX net_pkt (18902) time 63 us    [0->22->15->23=60 us]
Avg RX net_pkt (18892) time 42 us    [0->9->6->11->13=39 us]

The numbers inside the brackets contain information how many microseconds it took for a network packet to go from previous state to next.

In the TX example above, the values are averages over 18902 packets and contain this information:

  • Packet was created by application so the time is 0.

  • Packet is about to be placed to transmit queue. The time it took from network packet creation to this state, is 22 microseconds in this example.

  • The correct TX thread is invoked, and the packet is read from the transmit queue. It took 15 microseconds from previous state.

  • The network packet was just sent and the network stack is about to free the network packet. It took 23 microseconds from previous state.

  • In total it took on average 60 microseconds to get the network packet sent. The value 63 tells also the same information, but is calculated differently so there is slight difference because of rounding errors.

In the RX example above, the values are averages over 18892 packets and contain this information:

  • Packet was created network device driver so the time is 0.

  • Packet is about to be placed to receive queue. The time it took from network packet creation to this state, is 9 microseconds in this example.

  • The correct RX thread is invoked, and the packet is read from the receive queue. It took 6 microseconds from previous state.

  • The network packet is then processed and placed to correct socket queue. It took 11 microseconds from previous state.

  • The last value tells how long it took from there to the application. Here the value is 13 microseconds.

  • In total it took on average 39 microseconds to get the network packet sent. The value 42 tells also the same information, but is calculated differently so there is slight difference because of rounding errors.