The netlatency toolset is used to measure the latency and jitter parameters of an ethernet connection. The nl-tx generates UDP packets with embedded system timestamp (tx-user) and sequence number. The netlantency-rx captures these packets and dumps the collected receiving information such as timestamp from the linux network stack and the receiving system time (rx-user). nl-rx can detect receiving errors (dropped packets or sequence error).
The following timestamp values can be accessed on the nl-rx.
| Timestamp | Description |
|---|---|
| interval-start | The interval start timestamp |
| tx-wakeup | The wakeup timestamp of nl-tx |
| tx-program | The timestamp when calling the send function |
| tx-kernel-netsched | Linux kernel timestamp SOF_TIMESTAMPING_TX_SCHED |
| tx-kernel-driver | Linux kernel timestamp SOF_TIMESTAMPING_TX_SOFTWARE |
| rx-hardware | Linux kernel timestamp SOF_TIMESTAMPING_RX_HARDWARE |
| rx-program | Timestamp when handling the testpacket in nl-rx |
For linux kernel timestamp please refer to the kernel documentation:
https://www.kernel.org/doc/Documentation/networking/timestamping.txt
- libglib2.0-dev
- libjansson-dev
There is no byte order translation. Therefore, the sender and receiver application must run on the same CPU architecture.
Usage:
nl-tx [OPTION...] DEVICE - transmit timestamped test packets
Help Options:
-?, --help Show help options
Application Options:
-d, --destination Destination MAC address
-h, --histogram Create histogram data
-i, --interval Interval in milli seconds (default is 1000msec)
-c, --count Transmit packet count
-m, --memlock Configure memlock (default is 1)
-P, --padding Set the packet size
-p, --prio Set scheduler priority (default is 99)
-Q, --queue-prio Set skb priority
-v, --verbose Be verbose
-V, --version Show version inforamtion and exit
This tool sends ethernet test packets.
// not implemented yet
{
"type": "settings",
"object": {
"interval": 1000,
}
}
Usage:
-rx [OPTION...] DEVICE - receive timestamped test packets
Help Options:
-?, --help Show help options
Application Options:
-v, --verbose Be verbose
-q, --quiet Suppress error messages
-c, --count Receive packet count
-s, --socket Write packet results to socket
-h, --histogram Write packet histogram in JSON format
-e, --ethertype Set ethertype to filter(Default is 0x0808, ETH_P_ALL is 0x3)
-f, --rxfilter Set hw rx filterfilter
-p, --ptp Set hw rx filterfilter
-V, --version Show version inforamtion and exit
This tool receives and analyzes incoming ethernet test packets.
{
"type": "rx-packet",
"object": {
"sequence-number": 1,
"packet-size": 64,
"tx-user-timestamp": "",
"tx-user-target-timestamp": "",
"rx-hw-timestamp" "",
"rx-user-timestamp" "",
}
}
{
"type": "rx-packet",
"object": {
"sequence-number": 1,
"stream-id": result->stream_id,
"interval-usec": result->interval_usec,
"offset-usec": result->offset_usec,
"packet-size": result->packet_size,
"timestamps": {
"names": [
"interval-start":,
"tx-wakeup",
"tx-program",
"tx-kernel-netsched",
"tx-kernel-driver",
"rx-hardware",
"rx-kernel-driver",
"rx-program",
]
"values": [
<TIMESTAMP>,
<TIMESTAMP>,
<TIMESTAMP>,
<TIMESTAMP>,
<TIMESTAMP>,
<TIMESTAMP>,
<TIMESTAMP>,
<TIMESTAMP>,
],
}
}
}
{
"type": "rx-error",
"object": {
"dropped-packets": 1,
"sequence-error": true,
}
}
// not implemented yet
{
"type": "rx-packet-tx-timestamp",
"object": {
"sequence-number": 1,
"tx-hw-timestamp": "",
}
}
The nl-calc tool stores the testpacket results of nl-rx and builds information for histogram analysis. Including Application accurancy/latency, full transmit latency (from application to RX hardware) and rx jitter.
| Histogram type | Description |
|---|---|
| program-latency | Histogram data of program wakeup time. It is used to observe the application accuracy. |
| scheduled-times | Histogram data of packets runtime. |
| jitter | Histogram data of packets runtime in a smaller window with nanosecond resolution. |
The nl-report tool displays the data generated by nl-calc in graphs.
The nl-trace displays the output by nl-rx in a box-plot graphic. Each type of timestamp is collected and the data depicted. Hence a time distribution of the latency till the point of record can be seen.
For closer information about meaning of box-plot take a look at:
https://en.wikipedia.org/wiki/Box_plot
On receive servers site:
$ nl-rx enp2s0 -v | socat - udp-sendto:127.0.0.1:5000
On client site:
$ socat - udp4-listen:5000,reuseaddr,fork
$ nl-rx enp2s0 -c 10000 -v | nl-calc - | nl-report - /tmp/plot.png
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