Mask apt-daily timers in SPEC CPU profiles to prevent VC restarts on Ubuntu 24.04

[AlexWFMS]

Summary

Prepends a MaskAptDailyTimers ExecuteCommand dependency to the four SPEC CPU profiles (FPRATE, FPSPEED, INTRATE, INTSPEED) that masks apt-daily.timer, apt-daily-upgrade.timer, and their services on Linux (x64 + arm64).

Problem

On Ubuntu 24.04, running packed SPEC CPU workloads shows Virtual Client being killed mid-run between 06:00–07:00 UTC, desynchronizing packed workload results. The same experiment configuration on Ubuntu 22.04 does not reproduce.

Root cause chain:

1. Ubuntu 24.04 default-installs the needrestart package (22.04 does not). Its default config $nrconf{restart} = ''a'' auto-restarts services whose libraries were updated.
2. apt-daily-upgrade.timer fires at 06:00 UTC with RandomizedDelaySec=60min.
3. When it installs any package touching a library VC depends on (.NET, libc, openssl), needrestart kills VC via SIGTERM/SIGKILL, and systemd restarts it, producing a second Platform.Initialize event.

Evidence

Queried ~4,700 Ubuntu 24.04 VMs against the production WorkloadDiagnostics/JunoStaging clusters:

• 29% of Ubuntu 24.04 VMs show a mid-run VC restart.
• 0% on Ubuntu 22.04 (jammy), Windows, or focal in the same window.
• 80% of restarts at hour 6 UTC (3,835 of 4,768).
• Minute-of-hour distribution is uniform 0–59 — the signature of RandomizedDelaySec=60min.
• 94% of hour-6 restarts had a gap > 2h from the first Platform.Initialize (killed mid-run, not crash-at-start).
• No pre-restart VC error logs — consistent with external SIGKILL.

Change

{
    "Type": "ExecuteCommand",
    "Parameters": {
        "Scenario": "MaskAptDailyTimers",
        "SupportedPlatforms": "linux-x64,linux-arm64",
        "Command": "bash -c ''systemctl mask apt-daily.timer apt-daily-upgrade.timer apt-daily.service apt-daily-upgrade.service; systemctl stop apt-daily.timer apt-daily-upgrade.timer apt-daily.service apt-daily-upgrade.service; exit 0''"
    }
}

• SupportedPlatforms filter skips Windows.
• Wrapped in bash -c ''... ; exit 0'' so it is idempotent and non-fatal on non-Ubuntu Linux distros (CentOS/Suse/etc.) where the units do not exist.
• Placed as the first dependency so the timers are neutralized before the long SPEC runtime window.

Smoke test (Ubuntu 24.04.4 LTS Azure VM, Standard_D4s_v6)

Ran the exact Command string via az vm run-command:

• Baseline: needrestart 3.6-7ubuntu4.5 installed; both timers enabled/active; apt-daily-upgrade.timer next-run scheduled at 06:22:56 UTC (matches the observed restart window).
• After: systemctl is-enabled → masked for all four units; list-timers shows no next-run.
• Idempotent: second invocation also exited 0.
• stderr only contained the expected Created symlink /etc/systemd/system/... -> /dev/null lines.

Not changed

• PERF-SPECJBB.json / PERF-SPECJVM.json / PERF-GPU-SPECVIEW.json / POWER-SPEC*.json — left alone to keep this PR scoped to the four SPEC CPU 2017 profiles where the issue is reported. Can extend later if desired.
• needrestart config itself — masking the timer is a narrower fix than disabling needrestart globally.