How to verify if a CPU is truly dedicated: steal time, sysbench and stress-ng

A single benchmark run tells you nothing about the true nature of your CPU. This is the message from a technical post published today, 23 July 2026, on Contabo's blog, which proposes a three-step method to determine whether a VPS marketed as having a "dedicated CPU" is genuinely dedicated or, under sustained load, behaves like a shared instance.

The starting point is straightforward: a burstable and oversubscribed allocation can look fine in a 20-second snapshot, then throttle or fluctuate when subjected to longer workloads, or when other tenants on the same host start competing for CPU cycles.

Three tests, not one

The first check concerns CPU steal time—the metric that measures the percentage of time your vCPU wanted to run but the hypervisor allocated that cycle to another tenant. You can read this with top, or more granularly with mpstat -P ALL 1 60, or with extended sampling via sar -u 5 8640 to cover 12 hours at 5-second intervals.

The second test is sysbench, but run repeatedly: a single sysbench run tells you almost nothing; you need to run it multiple times at different hours, including during peak times, and examine the variance between runs rather than fixating on a single isolated number.

The third is an endurance test with stress-ng for a full hour (stress-ng --cpu $(nproc) --timeout 1h), which is useful because many shared VPS plans allow brief bursts of full power before throttling kicks in.

Reference thresholds

Metric	Dedicated CPU (pass)	Shared/oversubscribed (fail)
Steal time (%st)	0–1% constant, rare brief spikes	5–10%+ sustained, spikes exceeding 10% under load
Sysbench variance (20 runs)	Within a few percentage points, at any time of day	10%+ oscillations between runs, worse during peaks
Endurance stress-ng 1h	Flat performance throughout the hour	Throttling or frequency reduction after 5–10 minutes

Contabo applies this same method to its Max Performance VPS line, which features dedicated AMD EPYC cores as standard configuration rather than as an add-on option, with contracts from month to month up to 24 months. For those not yet ready to move to dedicated cores, the company recommends the Core VPS line as a starting point.

The commands listed above (top, mpstat, sar, sysbench, stress-ng) are available on any standard Linux distribution and replicable on any provider, not just Contabo.