User Guide


Back-End Bound

Metric Description

Back-End Bound metric represents a Pipeline Slots fraction where no uOps are being delivered due to a lack of required resources for accepting new uOps in the Back-End. Back-End is a portion of the processor core where an out-of-order scheduler dispatches ready uOps into their respective execution units, and, once completed, these uOps get retired according to program order. For example, stalls due to data-cache misses or stalls due to the divider unit being overloaded are both categorized as Back-End Bound. Back-End Bound is further divided into two main categories: Memory Bound and Core Bound.

Possible Issues

A significant proportion of pipeline slots are remaining empty. When operations take too long in the back-end, they introduce bubbles in the pipeline that ultimately cause fewer pipeline slots containing useful work to be retired per cycle than the machine is capable of supporting. This opportunity cost results in slower execution. Long-latency operations like divides and memory operations can cause this, as can too many operations being directed to a single execution port (for example, more multiply operations arriving in the back-end per cycle than the execution unit can support).

Product and Performance Information


Intel's compilers may or may not optimize to the same degree for non-Intel microprocessors for optimizations that are not unique to Intel microprocessors. These optimizations include SSE2, SSE3, and SSSE3 instruction sets and other optimizations. Intel does not guarantee the availability, functionality, or effectiveness of any optimization on microprocessors not manufactured by Intel. Microprocessor-dependent optimizations in this product are intended for use with Intel microprocessors. Certain optimizations not specific to Intel microarchitecture are reserved for Intel microprocessors. Please refer to the applicable product User and Reference Guides for more information regarding the specific instruction sets covered by this notice.

Notice revision #20110804