NVIDIA DOCA PCC Application Guide

This document provides a DOCA PCC implementation on top of NVIDIA® BlueField® DPU.

Programmable Congestion Control (PCC) allows users to design and implement their own congestion control (CC) algorithm, giving them the flexibility to work out an optimal solution to handle congestion in their clusters. On BlueField-3, PCC is provided as a component of DOCA.

The application leverages the DOCA PCC API to provide users the flexibility to manage allocation of DPA resources according to their requirements.

Typical DOCA application includes App running on host/Arm and App running on DPA. Developers are advised to use the host/Arm application with minimal changes and focus on developing their algorithm and integrating it into the DPA application.

sys-design-version-1-modificationdate-1702941523770-api-v2.png

DOCA PCC application consists of two parts:

  • Host/Arm app is the control plane. It is responsible for allocating all resources and handover to the DPA app initially, then destroying everything when the DPA app finishes its operation. The host app must always be alive to stay in control while the device app is working.

  • Device/DPA app is the data plane. It is mainly for CC event handler. When the first thread is activated, DPA App initialization is done in the DOCA PCC library by calling the algorithm initialization function implemented by the user in the app. Moreover, the user algorithm execution function is called when a CC event arrives. The user algorithm takes event data as input and performs a calculation using per-flow context and replies with updated rate value and a flag to sent RTT request.

The host/Arm application sends command to NIC firmware when allocating or destroying resources. CC events are generated by NIC hardware automatically when sending data or receiving ACK/NACK/CNP/RTT packets, then the device application handles these events by calling the user algorithm. After the DPA application replies to hardware, handling of current event is done and the next event can arrive.

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/opt/mellanox/doca/applications/pcc/src ├── host │ ├── pcc.c │ ├── pcc_core.c │ └── pcc_core.h └── device ├── algo │ ├── rtt_template.h │ ├── rtt_template_algo_params.h │ ├── rtt_template_ctxt.h │ └── rtt_template.c └── pcc_dev_main.c

The main content of the reference DOCA PCC application files are the following:

  • host/pcc.c – entry point to entire application

  • host/pcc_core.c – host functions to initialize and destroy the PCC application resources, parsers for PCC command line parameters

  • device/pcc_dev_main.c – callbacks for user CC algorithm initialization, user CC algorithm calculation, algorithm parameter change notification

  • device/algo/* – user CC algorithm reference template. Put user algorithm code here.

This application leverages the following DOCA library:

Refer to its respective programming guide for more information.

  • NVIDIA BlueField-3 DPU is required

  • Firmware 32.38.1000 and higher

  • MFT 4.25 and higher

Installation

Refer to the NVIDIA DOCA Installation Guide for Linux for details on how to install BlueField-related software.

Prerequisites

Enable USER_PROGRAMMABLE_CC in mlxconfig:

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mlxconfig -y -d /dev/mst/mt41692_pciconf0 set USER_PROGRAMMABLE_CC=1

R eset firmware or power cycle the host to apply the configuration change.

Warning

Make sure to perform graceful shutdown before power cycling the host.


Application Execution

The PCC application is provided in both source and binary forms. The binary is located under /opt/mellanox/doca/applications/pcc/bin/doca_pcc.

  1. Application usage instructions:

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    Usage: doca_pcc [DOCA Flags] [Program Flags]   DOCA Flags: -h, --help Print a help synopsis -v, --version Print program version information -l, --log-level Set the (numeric) log level for the program <10=DISABLE, 20=CRITICAL, 30=ERROR, 40=WARNING, 50=INFO, 60=DEBUG, 70=TRACE> --sdk-log-level Set the SDK (numeric) log level for the program <10=DISABLE, 20=CRITICAL, 30=ERROR, 40=WARNING, 50=INFO, 60=DEBUG, 70=TRACE> -j, --json <path> Parse all command flags from an input json file   Program Flags: -d, --device <IB device names>       IB device name that supports PCC (mandatory). -w, --wait-time <PCC wait time> The duration of the DOCA PCC wait (optional), can provide negative values which means infinity. If not provided then -1 will be chosen. -p, --pcc-threads <pcc-threads-list> A list of the PCC threads numbers to be chosen for the DOCA PCC context to run on (optional). Must be provided as a string, such that the number are separated by a space.

    Note

    This usage printout can be printed to the command line using the -h (or --help) options:

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    /opt/mellanox/doca/applications/pcc/bin/doca_pcc -h

    Note

    For additional information, refer to section "Command Line Flags".

  2. CLI example for running the application on the BlueField or the host:

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    /opt/mellanox/doca/applications/pcc/bin/doca_pcc -d mlx5_0

    Warning

    The IB device identifier (mlx5_0) should match the identifier of the desired IB device.

  3. The application also supports a JSON-based deployment mode, in which all command-line arguments are provided through a JSON file:

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    doca_pcc --json [json_file]

    For example:

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    cd /opt/mellanox/doca/applications/pcc/bin ./doca_pcc --json ./pcc_params.json

    Warning

    Before execution, ensure that the used JSON file contains the correct configuration parameters, and especially the PCIe addresses necessary for the deployment.

Command Line Flags

Flag Type

Short Flag

Long Flag/JSON Key

Description

JSON Content

General flags

h

help

Prints a help synopsis

N/A

v

version

Prints program version information

N/A

l

log-level

Sets the log level for the program:

  • DISABLE=10

  • CRITICAL=20

  • ERROR=30

  • WARNING=40

  • INFO=50

  • DEBUG=60

  • TRACE=70

N/A

N/A

sdk-log-level

Sets the log level for the program:

  • DISABLE=10

  • CRITICAL=20

  • ERROR=30

  • WARNING=40

  • INFO=50

  • DEBUG=60

  • TRACE=70

N/A

j

json

Parse all command flags from an input JSON file

N/A

Program flags

d

device

IB device name that supports PCC

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"device": ""

w

wait-time

(Optional) In seconds, the duration of the DOCA PCC wait. Negative values mean infinity.

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"wait-time": -1

p

pcc-threads

(Optional) A list of the PCC EU indexes to be chosen for the DOCA PCC event handler threads to run on. Must be provided as a string, such that the numbers are separated by a space.

The placement of the PCC threads per core can be controlled using the EU indexes. Utilizing a large number of EUs, while limiting the number of threads per core, gives the best event handling rate and lowest event latency.

The last EU is used for communication with the NIC while all others are for data path CC event handling.

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"pcc-threads": "176 177 178 179 180 181 182 183  184 185 186 187 192 193 194 195 196 197 198 199  200 201 202 203 208 209 210 211 212 213 214 215  216 217 218 219 224 225 226 227 228 229 230 231  232 233 234 235 240"

Note

Refer to DOCA Arg Parser for more information regarding the supported flags and execution modes.


Troubleshooting

Refer to the NVIDIA DOCA Troubleshooting Guide for any issue encountered with the installation or execution of the DOCA applications.

In addition to providing the application in binary form, the installation also includes all of the application sources and compilation instructions so as to allow modifying the sources and recompiling the application. For more information about the applications, as well as development and compilation tips, refer to the DOCA Applications page.

The sources of the application can be found under the /opt/mellanox/doca/applications/pcc/src directory.

Recompiling All Applications

The applications are all defined under a single meson project, so the default compilation recompiles all the DOCA applications.

To build all the applications together, run:

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cd /opt/mellanox/doca/applications/ meson /tmp/build ninja -C /tmp/build

Note

doca_pcc is created under /tmp/build/pcc/src/.


Recompiling PCC Application Only

To directly build only the PCC application:

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cd /opt/mellanox/doca/applications/ meson /tmp/build -Denable_all_applications=false -Denable_pcc=true ninja -C /tmp/build

Note

doca_pcc is created under /tmp/build/pcc/src/.

Alternatively, one can set the desired flags in the meson_options.txt file instead of providing them in the compilation command line:

  1. Edit the following flags in /opt/mellanox/doca/applications/meson_options.txt:

    • Set enable_all_applications to false

    • Set enable_pcc to true

  2. Run the following compilation commands :

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    cd /opt/mellanox/doca/applications/ meson /tmp/build ninja -C /tmp/build

    Note

    doca_pcc is created under /tmp/build/pcc/src/.

Troubleshooting

Refer to the NVIDIA DOCA Troubleshooting Guide for any issue encountered with the compilation of the application.

This section lists the application's configuration flow, explaining the different DOCA function calls and wrappers.

  1. Parse application argument.

    1. Initialize arg parser resources and register DOCA general parameters.

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      doca_argp_init();

    2. Register PCC application parameters.

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      register_pcc_params();

    3. Parse the arguments.

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      doca_argp_start();

      1. Parse DOCA flags.

      2. Parse DOCA PCC parameters.

  2. PCC initialization.

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    pcc_init();

    1. Open DOCA device that supports PCC.

    2. Create DOCA PCC context.

    3. Configure affinity of threads handling CC events.

  3. Start DOCA PCC.

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    doca_pcc_start();

    1. Create PCC process and other resources.

    2. Trigger initialization of PCC on device.

    3. Register the PCC in the NIC hardware so CC events can be generated and an event handler can be triggered.

  4. Process state monitor loop.

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    doca_pcc_get_process_state(); doca_pcc_wait();

    1. Get the state of the process:

      State

      Description

      DOCA_PCC_PS_ACTIVE = 0

      The process handles CC events (only one process is active at a given time)

      DOCA_PCC_PS_STANDBY = 1

      The process is in standby mode (another process is already ACTIVE)

      DOCA_PCC_PS_DEACTIVATED = 2

      The process has been deactivated by NIC firmware and should be destroyed

      DOCA_PCC_PS_ERROR = 3

      The process is in error state and should be destroyed

    2. Wait on process events from the device.

  5. PCC destroy.

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    doca_pcc_destroy();

    1. Destroy PCC resources. The process stops handling PCC events.

    2. Close DOCA device.

  6. Arg parser destroy.

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    doca_argp_destroy()

The Port Programmable Congestion Control (PPCC) register allows the user to configure and read PCC algorithms and their parameters/counters.

It supports the following functionalities:

  • Enabling different algorithms on different ports

  • Querying information of both algorithms and tunable parameters/counters

  • Changing algorithm parameters without compiling and reburning user image

  • Querying or clearing programmable counters

Usage

The PPCC register can be accessed using a string similar to the following:

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sudo mlxreg -d /dev/mst/mt41692_pciconf0 -y --get --op "cmd_type=0" --reg_name PPCC --indexes "local_port=1,pnat=0,lp_msb=0,algo_slot=0,algo_param_index=0" sudo mlxreg -d /dev/mst/mt41692_pciconf0 -y --set "cmd_type=1" --reg_name PPCC --indexes "local_port=1,pnat=0,lp_msb=0,algo_slot=0,algo_param_index=0"

Where you must:

  • Set the cmd_type and the indexes

  • Give values for algo_slot, algo_param_index

  • Keep local_port=1, pnat=0, lp_msb=0

  • Keep doca_pcc application running

cmd_type

Description

Method

Index

Input (in --set)

Output

0x0

Get algorithm info

Get

algo_slot

N/A

  • Value – 32-bit algo_num or 0 if no algo is available at this index

  • Text – algorithm description

  • sl_bitmask_support – indicates whether the device supports sl_bitmask logic

0x1

Enable algorithm

Set

sl_bitmask

trace_en

counter_en

N/A

0x2

Disable algorithm

Set

N/A

N/A

0x3

Get algorithm enabling status

Get

N/A

  • Value:

    • 0 – disabled

    • 1 – enabled

  • sl_bitmask – this field allows to apply to specific SLs based on the bitmask

  • sl_bitmask_support – indicates whether the device supports sl_bitmask logic

0x4

Get number of parameters

Get

N/A

  • Value – num of params of algo

0x5

Get parameter information

Get

algo_slot

algo_param_index

N/A

  • param_value1 – default value of param

  • param_value2 – min value of param

  • param_value3 – max value of param

  • prm –

    • 0: read-only

    • 1: read-write

    • 2: read-only but may be cleared using the "get and clear" command

0x6

Get parameter value

Get

N/A

  • Value – param value

0x7

Get and clear parameter

Get

N/A

  • Value – param value

0x8

Set parameter value

Set

Parameter value

N/A

0xA

Bulk get parameters

Get

algo_slot

N/A

  • text_length – param num x 4 bytes

  • text[0]…text[n] – param values

0xB

Bulk set parameters

Set

text_length - param num x 4

text[0]…text[n] - param values

N/A

0xC

Bulk get counters

Get

N/A

  • text_length – counter num x 4 bytes

  • text[0]…text[n] – counter values

0xD

Bulk get and clear counters

Get

N/A

  • text_length – counter num x 4 bytes

  • text[0]…text[n] – counter values

0xE

Get number of counters

Get

N/A

  • Value – num of counters of algo

0xF

Get counter information

Get

algo_slot

algo_param_index

N/A

  • param_value3 – max value of parameter

  • prm –

    • 0: read-only

    • 1: read-write

    • 2: read-only but may be cleared via "get & clear" command

0x10

Get algorithm info array

Get

N/A

N/A

  • text_length – algo slot initialized x 4 bytes

  • text[0]…text[n] – 32-bit algo_num or 0 if no algorithm is available at this slot index


Internal Default Algorithm

The internal default algorithm is used when enhanced connection establishment (ECE) negotiation fails. It is mainly used for backward compatibility and can be disabled using "force mode". Otherwise, users may change doca_pcc_dev_user_algo() in the device app to run a specific algorithm without considering the algorithm negotiation.

The force mode command is per port:

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sudo mlxreg -d /dev/mst/mt41692_pciconf0 -y --get --op "cmd_type=2" --reg_name PPCC --indexes "local_port=1,pnat=0,lp_msb=0,algo_slot=15,algo_param_index=0" sudo mlxreg -d /dev/mst/mt41692_pciconf0.1 -y --get --op "cmd_type=2" --reg_name PPCC --indexes "local_port=1,pnat=0,lp_msb=0,algo_slot=15,algo_param_index=0"


Counters

Counters are shared on the port and are only enabled on one algo_slot per port. The following command enables the counters while enabling the algorithm according to the algo_slot:

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sudo mlxreg -d /dev/mst/mt41692_pciconf0 -y --set "cmd_type=1,counter_en=1" --reg_name PPCC --indexes "local_port=1,pnat=0,lp_msb=0,algo_slot=0,algo_param_index=0"

After counters are enabled on the algo_slot, they can be queried using cmd_type 0xC or 0xD.

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sudo mlxreg -d /dev/mst/mt41692_pciconf0 -y --get --op "cmd_type=12" --reg_name PPCC --indexes "local_port=1,pnat=0,lp_msb=0,algo_slot=0,algo_param_index=0" sudo mlxreg -d /dev/mst/mt41692_pciconf0 -y --get --op "cmd_type=13" --reg_name PPCC --indexes "local_port=1,pnat=0,lp_msb=0,algo_slot=0,algo_param_index=0"


  • /opt/mellanox/doca/applications/pcc/src

  • /opt/mellanox/doca/applications/pcc/bin/pcc_params.json

© Copyright 2023, NVIDIA. Last updated on Feb 9, 2024.