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CPU contention is an event wherein individual CPU components and machines in a virtualized hardware system wait too long for their turn at processing. In such a system, resources (e.g., CPU, memory, etc.) are distributed between different virtual machines (VMs). As different processing resources are assigned to different machines, the schedulers in the system order the input/output and other tasks. The processing of these tasks is delayed when the machines assigned to them are experiencing a CPU contention.
Experts who look at CPU contention warn that this type of internal conflict can happen easily in a virtualized system. However, there are different ways to analyze the system to find out whether CPU contention is a problem. IT professionals look at the work of the VM kernel in handling the different processing demands. A metric called percent ready (%ready) shows how long a machine has to wait for processing power. When this number climbs too high, it indicates CPU contention.
There are also broader strategies for avoiding CPU contention; for example, experts suggest "building out" instead of clustering virtual CPU allocations in ways that can cause bottlenecks and contention issues. Generally, administrators want to look for high wait numbers and evidence that there are too many CPU components assigned for scheduling and that individual processes are delayed in ways that can inhibit performance.