Doca Pcc Ztr Rttcc Algo

DOCA PCC ZTR RTTCC Algorithm

Where to start: This skill assumes DOCA is already

installed, the user's BlueField has a DPA processor that

the host can see through DOCA (a BlueField-3-generation

device per the README), the BlueField firmware has the

custom-PCC slot enabled, the DPACC compiler is installed at

a matched version per the DOCA Compatibility Policy, and the

user is doing **hands-on deployment of the DOCA-shipped ZTR

RTTCC reference algorithm** on a BlueField port that

already carries RoCE-v2 traffic — i.e. either deploying it

as the no-config-required baseline, tuning its documented

parameters, or evaluating it against a custom algorithm the

user intends to write. Open TASKS.md if the

user wants to *do* something (install / configure / build /

modify / run / test / debug / use); open

CAPABILITIES.md when the question is

*what does the algorithm express, what are its variants and

parameters, what does it ship vs not ship*. If the user has

not installed DOCA yet, route to

doca-setup first; if the user

has not stood up the host-side doca-pcc framework yet,

route to doca-pcc first (this

algorithm is a *library consumed by* the PCC framework, not

a standalone program); if the user only wants to *inspect*

PCC counters at runtime without changing the running

algorithm, route to

doca-pcc-counters;

if the user wants to *write their own algorithm from

scratch*, that is the doca-pcc library plus the public

PCC programming guide — this skill is for the shipped

reference algorithm specifically.

Example questions this skill answers well

The CLASSES of ZTR RTTCC questions this skill is built to

answer, each with one worked example. The agent should

treat the *class* as the load-bearing piece — the worked

example is a single instance.

• **"Is the ZTR RTTCC reference algorithm the right

baseline for my deployment, or should I write a custom

algorithm?"** — worked example: *"I have a BlueField-3

carrying production RoCE-v2 traffic from a GPU cluster;

is the shipped algorithm a fine default or do I need

custom logic?"*. Answered by the decision rule in

CAPABILITIES.md ## Capabilities and modes

("when to use the reference vs custom") + the env

preconditions in

TASKS.md ## install.

• **"How do I wire the shipped algorithm into the DOCA

PCC application that's already running on my host?"** —

worked example: *"/opt/mellanox/doca/applications/pcc

is already building from sample sources; what do I

change so the user algo callback dispatches to

doca_pcc_dev_ztr_rttcc_algo under a chosen algo

slot?"*. Answered by the integration sequence in

CAPABILITIES.md ## Capabilities and modes

+ the in-place edits in

TASKS.md ## modify.

• **"Which variant of the algorithm am I getting — vanilla

RTT-CC, path-migration mode, RX-rate mode, multipath,

multipath with credits, window-probeless?"** — worked

example: *"the shipped library exposes one public

symbol doca_pcc_dev_ztr_rttcc_algo but the device-

side source ships several variants; how do I know

which one I get and how do I pick another?"*.

Answered by the variants table in

CAPABILITIES.md ## Capabilities and modes.

• **"How do I confirm the algorithm is actually

modulating my RDMA / RoCE traffic, and not just

loading?"** — worked example: *"I followed the

integration steps; the application starts; how do I

know the algorithm is shaping flows under load?"*.

Answered by the observability surface in

CAPABILITIES.md ## Observability

+ the counter-watch loop in

TASKS.md ## test which routes to

doca-pcc-counters.

• **"Which tunables does the algorithm expose, and how

do I change them from the host without rebuilding the

DPA-side image?"** — worked example: *"my workload is

more latency-sensitive than the default profile assumes

— which parameter knob do I adjust?"*. Answered by

the parameter surface in

CAPABILITIES.md ## Capabilities and modes

+ the doca_pcc_dev_set_ztr_rttcc_params workflow in

TASKS.md ## use.

• **"What does this DOCA_PCC_DEV_STATUS_FAIL or

DOCA_ERROR_* from a doca_pcc_dev_ztr_rttcc_* call

mean and which layer caused it?"** — worked example:

*"my init callback returns DOCA_PCC_DEV_STATUS_FAIL

on first launch"*. Answered by the algorithm overlay

on the host-side PCC taxonomy in

CAPABILITIES.md ## Error taxonomy

+ the layered ladder in

TASKS.md ## debug that escalates

through

doca-pcc and

doca-debug.

Audience

This skill serves **external developers operating a

BlueField-3-class DPU who want to deploy NVIDIA's shipped

reference PCC algorithm on RoCE-v2 traffic, OR who are

evaluating it against a custom algorithm they intend to

write**. The reference algorithm is *zero-touch* by design

— the no-config-required baseline — and the canonical use

case is dropping it onto a port and confirming it shapes

flows correctly under congestion. It is *not* for NVIDIA

developers contributing to the algorithm itself, nor for

users who want general PCC programming theory (route via

the public DOCA PCC programming guide), nor for users who

only want to *inspect* PCC counters (route to

doca-pcc-counters).

Language scope. The algorithm ships as a DPA-side

library (pkg-config module doca-pcc-ztr-rttcc-algo)

plus a public header doca_pcc_dev_ztr_rttcc_algo.h that

DPA-side translation units include. The shipped algorithm

binary is the static library

libdoca_pcc_ztr_rttcc_algo_dev.a per the README; the

device-side translation unit that consumes it is C and is

compiled by DPACC. The host-side that drives the PCC

context comes from doca-pcc;

this library does NOT add a host-side surface beyond the

host-side helpers (also shipped as

libdoca_pcc_ztr_rttcc_algo.{a,so} per the README) that

the doca-pcc framework links. Other-language host-side

wrappers around doca-pcc can drive this algorithm through

the same lifecycle described in doca-pcc; the DPA-side

integration always stays C-via-DPACC.

When to load this skill

Load this skill when the user is doing hands-on deployment,

tuning, or evaluation of the DOCA-shipped ZTR RTTCC

reference algorithm on a BlueField port carrying RoCE-v2

traffic, in any host language plus the DPA-side translation

unit built by dpacc. Concretely:

• Deciding whether the shipped algorithm is the right

baseline for the user's RoCE-v2 workload, or whether the

user needs a custom algorithm.

• Wiring the algorithm into the DOCA PCC sample

application by patching the user-algo / user-init /

user-set-algo-params callbacks per the steps the

shipped README documents.

• Picking which of the algorithm's documented variants

(vanilla, path-migration, RX-rate, RX-rate + PM,

multipath, multipath + credits, window-probeless)

matches the user's intent — and surfacing that the

*public* surface only ships one symbol

(doca_pcc_dev_ztr_rttcc_algo); the variants live in

the DPA-side source the user compiles against.

• Tuning the host-set parameters the algorithm exposes

(per the parameter list in

doca_pcc_dev_ztr_rttcc_algo.h and the shipped

doca_pcc_dev_set_ztr_rttcc_params).

• Observing whether the running algorithm is actually

modulating RoCE-v2 flows under load (route to

doca-pcc-counters

for the read-only inspection side).

• Deciding when to *replace* the shipped algorithm with a

custom one because latency target, fairness policy, or

convergence behavior requirements diverge from what the

reference provides.

Do not load this skill for general DOCA orientation;

for the host-side doca-pcc lifecycle (route to

doca-pcc); for writing a custom

algorithm from scratch (route to

doca-pcc and the public PCC

programming guide via

doca-public-knowledge-map);

for read-only PCC counter inspection (route to

doca-pcc-counters);

or for the default firmware-shipped PCC algorithms that

predate Programmable Congestion Control entirely (no

host-side code, no DPACC compile — that is a firmware-only

path routed via

doca-public-knowledge-map).

What this skill provides

This is a thin loader. The body keeps only the

orientation needed to pick the right next file. The

substantive algorithm-specific material lives in two

companion files:

• CAPABILITIES.md — what the shipped ZTR RTTCC

algorithm expresses on this version + this BlueField

generation + this firmware: the public DPA-side API

surface (doca_pcc_dev_ztr_rttcc_init,

doca_pcc_dev_ztr_rttcc_algo,

doca_pcc_dev_set_ztr_rttcc_params,

doca_pcc_dev_ztr_rttcc_get_param_num,

doca_pcc_dev_ztr_rttcc_get_counter_num,

doca_pcc_dev_ztr_rttcc_get_num_of_histograms), the

documented variants (vanilla / path-migration / RX-rate

/ multipath / window-probeless — pick one at

DPA-side compile time), the relationship to the

host-side doca-pcc framework (this is an algorithm

body the framework loads), the relationship to the

doca-pcc-counters tool (which is the canonical

inspection surface), the algorithm's parameter and

counter surface (RTT-based congestion signal,

per-feature parameter blocks), the error taxonomy in

DOCA_PCC_DEV_STATUS_OK / _FAIL, and the safety

policy.

• TASKS.md — step-by-step workflows for the in-scope

algorithm verbs: install, configure, build,

modify, run, test, debug, use. Plus a

Deferred task verbs block that points out-of-scope

questions at the right next skill.

The skill assumes DOCA + the DPACC compiler + the

doca-pcc host-side framework are

already installed; the BlueField is a generation that

exposes the DPA processor (the algorithm runs on the DPA);

the BlueField firmware has the custom-PCC slot enabled

(inherited from

doca-pcc CAPABILITIES.md ## Safety policy);

and the BlueField port the algorithm will modulate has

RoCE-v2 traffic actually flowing on it (the algorithm

modulates *existing* RDMA / RoCE traffic — without traffic,

there is nothing for it to do).

What this skill deliberately does not ship

This skill is agent guidance, not a samples or templates

bundle. To keep the boundary clean, it deliberately does not

contain — and pull requests should not add:

• The algorithm body itself, in any language. The

shipped algorithm is the static library

libdoca_pcc_ztr_rttcc_algo_dev.a (plus the host-side

helpers) installed by the matching DOCA host package

per the README. The agent's job is to route the user to

the installed library and header

(doca_pcc_dev_ztr_rttcc_algo.h) and to prescribe the

in-place edits documented in the README on the

shipped DOCA PCC application source, not to author the

algorithm.

• A standalone PCC application. The DOCA PCC

application that hosts this algorithm is the shipped

C sample under

/opt/mellanox/doca/applications/pcc/ (per the

README). The agent's job is to prescribe the

minimum-diff modifications the README documents and to

walk the user through the rebuild — not to author a

parallel application.

• **A description of every internal variant's

behavior.** The DPA-side source ships several

variants (vanilla, path-migration, RX-rate, multipath,

multipath + credits, window-probeless). The agent

names the variant set, says which one is reachable via

the public symbol on this install, and routes

algorithm-design questions to the public PCC

programming guide via

doca-public-knowledge-map.

It does not redefine each variant's mathematical

behavior.

• A specific congestion-control algorithm tutorial.

Congestion-control theory, RoCE-v2 fairness analysis,

workload-specific tuning — out of scope. Route to the

user's own domain expertise and to the public DOCA PCC

guide.

Loading order

• Read this SKILL.md first to confirm the user's

question is in scope (deployment / tuning / evaluation

of the shipped reference algorithm, not algorithm

design from scratch and not read-only counter

inspection).

• **For the algorithm capability matrix, the public

DPA-side API surface, the variant set, the parameter

and counter surface, the host-side doca-pcc

framework relationship, the

doca-pcc-counters inspection-side relationship, the

error taxonomy, the observability surface, and the

safety policy, see CAPABILITIES.md.**

• **For step-by-step workflows — install, configure,

build, modify, run, test, debug, use — see

TASKS.md.**

Both companion files cross-link to each other,

doca-pcc for the host-side PCC

lifecycle that loads this algorithm,

doca-pcc-counters

for the read-only counter-inspection side of validating that

the algorithm is modulating traffic,

doca-dpa for the DPA-side

two-side-program model and the DPACC compiler discipline,

doca-version for the

canonical DOCA version-handling rules (with the DPACC

overlay inherited from

doca-dpa and

doca-pcc), and

doca-public-knowledge-map

whenever the right answer is "look it up in the public DOCA

PCC programming guide or the on-disk install layout".

Related skills

• doca-pcc — the host-side PCC

control library. This algorithm is loaded INTO a

doca_pcc context that doca-pcc stands up; the

host-side lifecycle (doca_pcc create / configure /

start / stop / destroy, the algorithm image

doca_pcc_app, the attach-to-port semantics) is owned

by doca-pcc. This skill prescribes only the DPA-side

algorithm integration on top.

• doca-pcc-counters —

the read-only diagnostic CLI for PCC counters at the

port. The canonical *"is the algorithm actually

modulating traffic"* check goes through the counter

tool; this skill names what counters the algorithm

emits (CNP / NACK / AI / HAI / decrement / RTT-band

counters per the public header) and routes the

inspection workflow to the tool skill.

• doca-dpa — the host-side

DPA control library. The algorithm runs on the DPA,

compiled by DPACC; the two-side-program rule and the

DOCA-and-DPACC version-match overlay inherited from

here apply.

• doca-public-knowledge-map —

the routing table for every public DOCA documentation

source (the DOCA PCC programming guide at

<https://docs.nvidia.com/doca/sdk/doca-pcc/index.html>;

the DOCA PCC application guide; the DOCA Compatibility

Policy) and the on-disk layout of an installed DOCA

package.

• doca-setup — env

preparation, install verification, DPACC compiler

install / verification, BlueField firmware

configuration (including the custom-PCC slot enable),

and the *I have no install yet* path with the public

NGC DOCA container. This skill assumes its

preconditions are satisfied AND that DPACC is installed

at a version that matches DOCA AND that the firmware-

level custom-PCC slot is enabled.

• doca-version —

canonical DOCA version-handling rules. This skill's

## Version compatibility cross-links the four-way

match rule plus the DOCA-and-DPACC overlay inherited

from doca-pcc.

• doca-structured-tools-contract —

the bundle's structured-tools precedence rule (detect /

prefer / fall back / report). The Command appendix in

TASKS.md honors this contract.

• doca-programming-guide —

general DOCA programming patterns. This skill layers

algorithm-specific overlays on top of the universal

build, modify-a-shipped-sample, and Core lifecycle

patterns.

• doca-debug — cross-cutting

debug ladder. Algorithm-specific debug (the algorithm

loaded but counters do not move; the algorithm fails to

initialize; the algorithm modulates traffic too

aggressively / too gently for the workload) overlays on

top of that ladder.

• doca-hardware-safety —

cross-cutting hardware-safety meta-policy. Because the

algorithm modulates production RoCE-v2 flows on a

BlueField port, the meta-policy's pre-flight inventory,

replica-first, and rollback rules apply via this

skill's ## Safety policy overlay.