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kernel-mshv: CONFIG_PSI was dropped in the dom0 v2411.19.1 config update

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Assessment

Difficulty
2/5
Estimated time
1-3 hours
Newbie friendliness
72/100
Issue type
Bug
Clarity
Clearly specified
Activity status
Active
Tech stack
linux
Domain
operating-systems

Research direction

Start by reading SPECS/kernel-mshv/config and the source defconfig mentioned in the issue, then compare the PSI setting with the history around #9720, #13648, and #17187. Restore CONFIG_PSI=y in the relevant configuration if the regression is confirmed, and verify the built kernel config and /proc/pressure/{cpu,io,memory} as described in the reproduction steps.

Written by the indexing model from the issue text.

Description

Environment

  • Azure Linux version and/or image name: 3.0, AKS Azure Linux 3 Kata (Pod Sandboxing) node image 202610.08.0
  • Kernel version: 6.6.137.mshv2-2.azl3
  • Architecture: x86_64
  • Affected package(s) and version(s), if applicable: kernel-mshv 6.6.137.mshv2-2.azl3
  • Custom image or package modifications, if applicable: none

Deployment / platform

  • Azure VM
  • AKS
  • Azure Linux container image
  • Other (please describe)

Describe the bug
kernel-mshv is built without CONFIG_PSI, so Kata hosts have no pressure stall information (/proc/pressure/* and the cgroup v2 *.pressure files are absent).

PSI was enabled for this kernel in #9720 ("kernel-mshv: enable CONFIG_PSI for cgroup-memory-telemetry"). It was then removed by #13648 ("dom0 packages: Update to dom0 release v2411.19.1"): the parent of that commit has CONFIG_PSI=y in SPECS/kernel-mshv/config, and the commit itself has # CONFIG_PSI is not set. The PR doesn't mention PSI, so this looks like an unintended regression from the config update rather than a deliberate change. #17187 later restored several other options but not PSI.

Steps to reproduce

  1. Boot a node running kernel-mshv 6.6.137.mshv2-2.azl3 (for example, an AKS Kata node pool).
  2. Run grep CONFIG_PSI /boot/config-$(uname -r) and ls /proc/pressure /sys/fs/cgroup/cpu.pressure.

Expected behavior
CONFIG_PSI=y, as after #9720 and as in the standard Azure Linux 3 kernel, so /proc/pressure/{cpu,io,memory} exist.

Actual behavior

# CONFIG_PSI is not set
ls: cannot access '/proc/pressure': No such file or directory
ls: cannot access '/sys/fs/cgroup/cpu.pressure': No such file or directory

No psi= parameter is on the kernel command line; because the option is compiled out, it can't be enabled at boot.

Additional context
Impact on AKS Kata hosts: Prometheus node-exporter's pressure collector returns no data (node_scrape_collector_success{collector="pressure"} 0, no node_pressure_* series), and node health checks that rely on CPU/memory pressure can't use PSI. Other kernel-mshv users who rely on PSI (including the cgroup memory telemetry that motivated #9720) are likely affected too.

Could CONFIG_PSI=y be restored, along with its source defconfig, so a future dom0 sync doesn't drop it again? If PSI was intentionally disabled for dom0, could you share the reason so we can document the expected behavior?

Dominant language
Python
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Merged PRs (30d)
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