A collection of one or more threads that is ready but not able to run on the processor due to another active thread that is currently running is called the processor queue. The clearest symptom of a processor bottleneck is a sustained or recurring queue of more than two threads. Although queues are most likely to develop when the processor is very busy, they can develop when utilization is well below 90 percent. This can happen if requests for processor time arrive randomly and if threads demand irregular amounts of time from the processor.
The number of threads in the processor queue. Shows ready threads only, not threads that are running. Even multiprocessor computers have a single queue for processor time; thus, for multiprocessors, you need to divide this value by the number of processors servicing the workload. A sustained processor queue of less than two threads per processor is normally acceptable, depending upon the workload.
Different guidelines apply for queue lengths on multiprocessor systems. For busy systems (those having processor utilization in the 80 to 90 percent range) that use thread scheduling, the queue length should range from one to three threads per processor. For example, on a four-processor system, the expected range of processor queue length on a system with high CPU activity is 4 to 12.
On systems with lower CPU utilization, the processor queue length is typically 0 or 1.
Our System Monitor II gadget can show you your CPU queue length in a real time.
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