This metric represents a fraction of cycles when the CPU was stalled due to switches of uop delivery to the Microcode Sequencer (MS). Commonly used instructions are optimized for delivery by the DSB or MITE pipelines. Certain operations cannot be handled natively by the execution pipeline, and must be performed by microcode (small programs injected into the execution stream). Switching to the MS too often can negatively impact performance. The MS is designated to deliver long uOp flows required by CISC instructions like CPUID, or uncommon conditions like Floating Point Assists when dealing with Denormals.