PCC

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 good 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 DOCA PCC application provides users the flexibility to manage allocation of DPA resources according to their needs. The application leverages the DOCA PCC library to generate an executable binary file.

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.

system-design-diagram.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 libraries:

  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 all registered parameters.
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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();

  1. Refer to the following documents:
  2. The pre-built PCC binary is located under /opt/mellanox/doca/applications/pcc/bin/doca_pcc. To build all the applications together, run:
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    cd /opt/mellanox/doca/applications/ meson /tmp/build ninja -C /tmp/build


  3. To build only the allreduce application:
    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 commands in step 2.
      Note:

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

  4. Pre-run setup:
    1. Enable USER_PROGRAMMABLE_CC in mlxconfig:
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      mlxconfig -y -d /dev/mst/mt41692_pciconf0 set USER_PROGRAMMABLE_CC=1

    2. Reset firmware or power cycle the host.
  5. Running the application on the host or BlueField, CLI example:
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    /opt/mellanox/doca/applications/pcc/bin/doca_pcc -d mlx5_0

    Application usage:
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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 log level for the program <CRITICAL=20, ERROR=30, WARNING=40, INFO=50, DEBUG=60> 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.

    For additional information on available flags, use -h:
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    /opt/mellanox/doca/applications/pcc/bin/doca_pcc -h


  6. To run doca_pcc using 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

Refer to NVIDIA DOCA Arg Parser Programming Guide for more information.
Flag Type Short Flag Long Flag/JSON Key Description JSON Content
General flags l log-level Set the log level for the application:
  • CRITICAL=20
  • ERROR=30
  • WARNING=40
  • INFO=50
  • DEBUG=60
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"log-level": 60

v version Print program version information N/A
h help Print a help synopsis 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 183184 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"


The Port Programmable Congestion Control (PPCC) register allows the user to configure and read PCC algorithm parameters.

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

8.1. 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 Get 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

8.2. 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"

8.3. 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

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