12. DPDK Telemetry User Guide

The Telemetry library provides users with the ability to query DPDK for telemetry information, currently including information such as ethdev stats, ethdev port list, and eal parameters.

12.1. Telemetry Interface

The Telemetry Library opens a socket with path <runtime_directory>/dpdk_telemetry.<version>. The version represents the telemetry version, the latest is v2. For example, a client would connect to a socket with path /var/run/dpdk/*/dpdk_telemetry.v2 (when the primary process is run by a root user).

12.2. Telemetry Initialization

The library is enabled by default, however an EAL flag to enable the library exists, to provide backward compatibility for the previous telemetry library interface:

--telemetry

A flag exists to disable Telemetry also:

--no-telemetry

12.3. Running Telemetry

The following steps show how to run an application with telemetry support, and query information using the telemetry client python script.

Launch testpmd as the primary application with telemetry:
```
./app/dpdk-testpmd
```
Launch the telemetry client script:
```
./usertools/dpdk-telemetry.py
```

When connected, the script displays the following, waiting for user input:

Connecting to /var/run/dpdk/rte/dpdk_telemetry.v2
{"version": "DPDK 20.05.0-rc2", "pid": 60285, "max_output_len": 16384}
-->

The user can now input commands to send across the socket, and receive the response. Some available commands are shown below.
- List all commands:
```
--> /
{"/": ["/", "/eal/app_params", "/eal/params", "/ethdev/list",
"/ethdev/link_status", "/ethdev/xstats", "/help", "/info"]}
```
- Get the list of ethdev ports:
```
--> /ethdev/list
{"/ethdev/list": [0, 1]}
```
Note

For commands that expect a parameter, use “,” to separate the command and parameter. See examples below.
- Get extended statistics for an ethdev port:
```
--> /ethdev/xstats,0
{"/ethdev/xstats": {"rx_good_packets": 0, "tx_good_packets": 0,
"rx_good_bytes": 0, "tx_good_bytes": 0, "rx_missed_errors": 0,
...
"tx_priority7_xon_to_xoff_packets": 0}}
```
- Get the help text for a command. This will indicate what parameters are required. Use the help keyword followed by the command or keyword of interest, for example:
```
--> help FOREACH
FOREACH usage:
   FOREACH /<list_cmd> /<iter_cmd> .<field> [.<field> ...]
   FOREACH <var> /<list_cmd> /<iter_cmd_with_$var> .<field> [.<field> ...]

Examples:
   FOREACH /ethdev/list /ethdev/stats .opackets
   ...

--> help /ethdev/xstats
{"/help": {"/ethdev/xstats": "Returns the extended stats for a port. Parameters: int port_id"}}
```
Note

For commands starting with / that are telemetry endpoints, the help text can also be obtained by sending the /help command to the telemetry socket. In this case, the parameter must be separated by a comma, not a space. For example:
```
--> /help,/ethdev/xstats
{"/help": {"/ethdev/xstats": "Returns the extended stats for a port. Parameters: int port_id"}}
```
- Run a compound query using FOREACH.
  
  The FOREACH command runs a list command, iterates each returned item, runs a second command for each item, and emits combined JSON output.
  
  Start with the simplest form (no loop variable):
```
FOREACH /<list_cmd> /<iter_cmd> .<field> [.<field> ...]
```
  To include numbered output, use a loop variable:
```
FOREACH <var> /<list_cmd> /<iter_cmd_with_$var> .<field> [.<field> ...]
```
  Notes:
  - Field selectors are whitespace-separated tokens, each starting with ..
  - In no-variable mode, the iter command is called as /<iter_cmd>,<item>.
  - In loop-variable mode, use $<var> in the iter command where the item value should be substituted.
  Examples:
```
--> FOREACH /ethdev/list /ethdev/stats .opackets
[0, 0]

--> FOREACH /ethdev/list /ethdev/stats .ipackets .opackets
[{"ipackets": 0, "opackets": 0}, {"ipackets": 0, "opackets": 0}]

--> FOREACH i /ethdev/list /ethdev/info,$i .name
[{"i": 0, "name": "0000:16:00.0"}, {"i": 1, "name": "0000:16:00.1"}]

--> FOREACH i /ethdev/list /ethdev/stats,$i .ipackets .opackets
[{"i": 0, "ipackets": 0, "opackets": 0}, {"i": 1, "ipackets": 0, "opackets": 0}]
```
  Output behavior:
  - Without loop variable and one field: returns an array of values.
  - Without loop variable and multiple fields: returns an array of objects containing named value fields.
  - With loop variable: returns an array of objects containing the loop variable field and requested value fields.
- Use command aliases.
  
  The telemetry script can load aliases at startup from:
```
$XDG_CONFIG_HOME/dpdk/telemetry_aliases
```
  If XDG_CONFIG_HOME is not set, $HOME/.config/dpdk/telemetry_aliases is used. A custom path can also be provided via the --alias-file script flag.
  
  Each alias entry must be in alias=command format. Empty lines and lines starting with # are ignored.
  
  Example alias file:
```
# Basic shortcuts
ls=/ethdev/list
names=FOREACH i /ethdev/list /ethdev/info,$i .name
q=quit
```
  Alias behavior is intentionally similar to shell aliases:
  - The first token of the entered input is checked for an alias match.
  - If matched, that first token is replaced with its expansion.
  - Alias expansion is recursive (aliases can expand to other aliases).
  - Expansion has a safety limit to prevent infinite loops.
  Examples:
```
--> ls
{"/ethdev/list": [0, 1]}

--> names
[{"i": 0, "name": "0000:16:00.0"}, {"i": 1, "name": "0000:16:00.1"}]

--> q
# exits the client
```

12.4. Connecting to Different DPDK Processes

When multiple DPDK process instances are running on a system, the user will naturally wish to be able to select the instance to which the connection is being made. The method to select the instance depends on how the individual instances are run:

For DPDK processes run using a non-default file-prefix, i.e. using the –file-prefix EAL option flag, the file-prefix for the process should be passed via the -f or –file-prefix script flag.

For example, to connect to testpmd run as:
```
$ ./build/app/dpdk-testpmd -l 2,3 --file-prefix="tpmd"
```
One would use the telemetry script command:
```
$ ./usertools/dpdk-telemetry -f "tpmd"
```
To list all running telemetry-enabled file-prefixes, the -l or --list flags can be used:
```
$ ./usertools/dpdk-telemetry -l
```
For the case where multiple processes are run using the –in-memory EAL flag, but no –file-prefix flag, or the same –file-prefix flag, those processes will all share the same runtime directory. In this case, each process after the first will add an increasing count suffix to the telemetry socket name, with each one taking the first available free socket name. This suffix count can be passed to the telemetry script using the -i or –instance flag.

For example, if the following two applications are run in separate terminals:
```
$ ./build/app/dpdk-testpmd -l 2,3 --in-memory    # will use socket "dpdk_telemetry.v2"

$ ./build/app/test/dpdk-test -l 4,5 --in-memory  # will use "dpdk_telemetry.v2:1"
```
The following telemetry script commands would allow one to connect to each binary:
```
$ ./usertools/dpdk-telemetry.py       # will connect to testpmd

$ ./usertools/dpdk-telemetry.py -i 1  # will connect to test binary
```