[bart0sh]

Publishing PCIe roots on topology-aware DRA devices

Ninth PR of the DRA series, on top of #829. Four commits.

Each topology-aware DRA device now has the standard resource.kubernetes.io/pcieRoot attribute: the PCIe roots of the device's CPU socket. With it, a claim can use matchAttribute to get CPUs and a device of another driver, such as a NIC, under the same PCIe root.

Which roots a device lists

The kernel reports the CPUs local to a PCIe root in /sys/devices/pciDDDD:BB/pci_bus/DDDD:BB/cpulistaffinity. It computes them from the NUMA node of the root. With sub-NUMA clustering, this is one zone of the socket, but the root is equally close to all zones of the socket. So sysfs discovery gives a root to every package that its local CPUs are in. Every NUMA device of a package lists all the roots of that package.

For example, on a two-socket machine with SNC2, so four NUMA nodes, root pci0000:5d reports only the CPUs of node 2. Nodes 0 and 2 both list pci0000:00, pci0000:17, pci0000:3a and pci0000:5d.

CPUPackage.PCIeRoots() returns the roots of a package, sorted. A root whose cpulistaffinity cannot be read is skipped.

Clusters without list attributes

pcieRoot is a list attribute. List attributes need the DRAListTypeAttributes feature gate (KEP-5491), which is alpha and off by default. Without the gate, the API server rejects the whole ResourceSlice, so no devices would be published at all.

A driver cannot read the gate, so the DRA plugin asks the API server. When the plugin is created, it does a server-side dry run of a slice with a list attribute. Any failure counts as no support. Policies get the result from Owner.DRAListAttributesSupported(), and topology-aware leaves pcieRoot out without support. The driver itself still does not look at device attributes.

A slice with list attributes holds at most 64 devices, not 128. The plugin now always splits the devices into slices of 64.

What is not here

• The probe runs once, when the plugin starts. If the feature gate changes later, the plugin needs a restart to see it.
• Claims do not survive a restart, and no DeviceClass ships yet, as in the earlier PRs of the series.

Verification

• go test -race passes for sysfs, resmgr, the DRA plugin and the template, balloons and topology-aware policies, and golangci-lint finds no issues.
• TestRecordedPCIeRoots checks the roots of each package in the recorded sample. TestDiscoverPCIeRoots also covers a root reporting CPUs of both sockets, a root in no package, and roots that cannot be read.
• TestProbeListAttributes covers an accepted, a rejected and a failed probe, and checks that the probe is a dry run.
• TestDRAPCIeRoots checks that no roots are published without support, and that the roots of package 0 appear on its two NUMA nodes once there is support.
• test43-dra-pcie-roots and test42-dra-devices pass on n4c16 with Kubernetes 1.37 and containerd v2.4.1, with and without DRAListTypeAttributes. With the gate, every device lists the only root of the VM, pci0000:00. Without it, the devices are published without pcieRoot.
• The discovery also ran on the real two-socket SNC2 machine, and gave the same roots as the recorded sample.

[Copilot]

🟢 Approval recommended

Discovery, compatibility probing, publication, and slice sizing are consistently implemented and well tested.

0 open findings

What changed in this PR

Adds PCIe-root topology attributes to topology-aware DRA devices while remaining compatible with clusters lacking list-attribute support.

Changes:

• Discovers and maps PCIe roots to CPU packages.
• Probes API-server support for list attributes and publishes roots conditionally.
• Adds unit, recorded-sysfs, and end-to-end coverage.

File	Description
pkg/​sysfs/​system.go	Discovers package-local PCIe roots.
pkg/​sysfs/​pcie_test.go	Tests PCIe-root discovery edge cases.
pkg/​sysfs/​system_test.go	Verifies recorded root topology.
pkg/​sysfs/​test-setup.sh	Extracts the new sample.
pkg/​sysfs/​test-data-sample3.tar.xz	Provides recorded SNC topology.
pkg/​resmgr/​dra/​plugin.go	Probes list support and limits slice size.
pkg/​resmgr/​dra/​plugin_test.go	Tests probing and slice splitting.
pkg/​resmgr/​dra.go	Exposes probe results to policies.
pkg/​resmgr/​policy/​policy.go	Extends the policy-owner contract.
cmd/​plugins/​topology-aware/​policy/​dra.go	Publishes PCIe-root attributes.
cmd/​plugins/​topology-aware/​policy/​dra_test.go	Tests conditional root publication.
cmd/​plugins/​topology-aware/​policy/​mocks_test.go	Updates package mocks.
cmd/​plugins/​topology-aware/​policy/​coldstart_test.go	Updates the test owner interface.
test/​e2e/​policies.test-suite/​topology-aware/​n4c16/​test43-dra-pcie-roots/​code.var.sh	Verifies cluster-level publication behavior.

🧠 Review effort: Balanced

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[klihub]

LGTM

[askervin]

LGTM