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A VM process can have less CPU capacity than its vCPU count and host-wide utilisation imply. When its cgroup is being throttled, adding another IO thread cannot create CPU capacity and can instead drive repeated, counterproductive scale-up decisions. Resolve each process's cgroup v2 path, read its `cpu.max` quota and `cpu.stat` throttle counters, and retain the latest sample on the instance. The threshold engine can then hold scale-up whenever `throttled_usec` increased since the preceding sample. The first refresh always establishes an initial sample. The optional `refresh_cgroup_on_each_read` setting refreshes quota and counters on every tick when operators need runtime cgroup changes reflected immediately; leaving it disabled avoids repeated filesystem reads for stable production placement. Component-test configuration explicitly disables both refresh and cgroup-based scale-up blocking where the fake process does not model cgroups. Signed-off-by: Thanos Makatos <thanos.makatos@nutanix.com>
tmakatos
added this pull request to stack #43
September 24, 2026 21:44
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A VM process can have less CPU capacity than its vCPU count and
host-wide utilisation imply. When its cgroup is being throttled, adding
another IO thread cannot create CPU capacity and can instead drive
repeated, counterproductive scale-up decisions.
Resolve each process's cgroup v2 path, read its
cpu.maxquota andcpu.statthrottle counters, and retain the latest sample on theinstance. The threshold engine can then hold scale-up whenever
throttled_usecincreased since the preceding sample.The first refresh always establishes an initial sample. The optional
refresh_cgroup_on_each_readsetting refreshes quota and counters onevery tick when operators need runtime cgroup changes reflected
immediately; leaving it disabled avoids repeated filesystem reads for
stable production placement. Component-test configuration explicitly
disables both refresh and cgroup-based scale-up blocking where the fake
process does not model cgroups.
Signed-off-by: Thanos Makatos thanos.makatos@nutanix.com
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