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fix(aggregator): prevent CPU cores overflow when processes restart
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Guard against unsigned integer underflow in cgroup CPU calculation.
When processes exit and new ones start, totalTicks can be less than
the previous value, causing the subtraction to wrap around to a huge
positive number.

Now checks totalTicks >= prev before calculating delta, treating
process churn as 0 CPU usage for that sample.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
This commit is contained in:
Manuel Ganter 2026-02-06 15:15:30 +01:00
parent 5b983692c8
commit 0af8c28bc2
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1 changed files with 8 additions and 3 deletions
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11
internal/metrics/aggregator.go
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@ -348,9 +348,14 @@ func (a *Aggregator) calculateCgroupMetrics(
// Calculate CPU cores used from delta
usedCores := 0.0
if prev, ok := a.prevCgroupCPU[containerName]; ok && elapsed > 0 {
deltaTicks := totalTicks - prev
// Convert ticks to cores: deltaTicks / (elapsed_seconds * CLK_TCK)
usedCores = float64(deltaTicks) / (elapsed * float64(proc.DefaultClockTicks))
// Guard against underflow: if processes exited and new ones started,
// totalTicks could be less than prev. In that case, skip this sample.
if totalTicks >= prev {
deltaTicks := totalTicks - prev
// Convert ticks to cores: deltaTicks / (elapsed_seconds * CLK_TCK)
usedCores = float64(deltaTicks) / (elapsed * float64(proc.DefaultClockTicks))
}
// If totalTicks < prev, usedCores stays 0 for this sample
}
a.prevCgroupCPU[containerName] = totalTicks