The CPU Usage metric shows the percentage of CPU utilised on each of the Redis nodes. The percentage shown is the percentage of total CPU available (ie the maximum possible is 100% no matter how many CPU cores in the node).
High CPU usage is one indicator of a node reaching the limits of its processing capacity. One such example is the usage of CPU intensive operations such as smembers.
Please contact Instaclustr Support should you have any questions regarding this metric or the processing capacity of your cluster.