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license: Apache-2.0 name: doca-pcc-ztr-rttcc-algo description: > Use this skill when the user is doing hands-on deployment, tuning, or evaluation of the DOCA-shipped Zero-Touch RoCE RTT-based Congestion Control (ZTR RTTCC) reference algorithm on a BlueField-3 DPA — wiring doca_pcc_dev_ztr_rttcc_algo into the shipped DOCA PCC sample, picking a variant (vanilla / PM / RX-rate / multipath / window-probeless) at DPACC build time, tuning host-set parameters, or diagnosing DOCA_PCC_DEV_STATUS_FAIL from the algorithm. Trigger even when the user does not say 'DOCA PCC' or 'ZTR RTTCC' — typical implicit phrasings: 'my RoCE-v2 flows aren't being throttled', 'PCC sample isn't dispatching to my algo', 'how do I pick the multipath PCC variant', 'set-params returns fail', 'algorithm loaded but counters are flat', or 'do I need a custom CC algorithm on BF3'. Refuse and route elsewhere for writing a custom PCC algorithm from scratch, read-only PCC counter inspection, the host-side doca-pcc lifecycle, or firmware-only pre-Programmable PCC — those belong to other skills. metadata: kind: library compatibility: > Requires DOCA SDK installed at /opt/mellanox/doca on Linux (Ubuntu 22.04/24.04 or RHEL/SLES) with a BlueField-3 DPU exposing the DPA processor, the firmware custom-PCC slot enabled, a matched-version DPACC compiler, and live RoCE-v2 traffic on the attached port. Reads pkg-config doca-pcc-ztr-rttcc-algo and inspects /opt/mellanox/doca/{lib,include,applications/pcc}.

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 e