The CPUs statistic is used to display the heat map for CPUs broken down by percent utilization. This is the most accurate way to examine how CPUs are utilized.
When to Check CPUs
When investigating CPU load, after checking the utilization average from CPU: Percent Utilization.
This statistic is particularly useful for identifying if a single CPU is fully utilized, which can happen if a single thread is saturated with load. If the work performed by this thread cannot be offloaded to other threads so that it can be run concurrently across multiple CPUs, then that single CPU can become the bottleneck. This will be seen as a single CPU stuck at 100% utilization for several seconds or more, while the other CPUs are idle.
Table 6-1 A Breakdown of CPUs
A heat map with utilization on the Y-axis and each level on the Y-axis colored by the number of CPU at that utilization: from light (none) to dark (many).
CPU utilization includes the time to process instructions (that are not part of the idle thread), which includes memory stall cycles. CPU utilization can be caused by:
Executing code (including spinning on locks)
Because Oracle ZFS Storage Appliance primarily exists to move data, memory load often dominates. Therefore, a system with high CPU utilization might actually be high when it is moving data.