User Guide

Contents

Assists

Metric Description

This metric estimates cycles fraction the CPU retired uops delivered by the Microcode_Sequencer as a result of Assists. Assists are long sequences of uops that are required in certain corner-cases for operations that cannot be handled natively by the execution pipeline. For example, when working with very small floating point values (so-called Denormals), the FP units are not set up to perform these operations natively. Instead, a sequence of instructions to perform the computation on the Denormals is injected into the pipeline. Since these microcode sequences might be hundreds of uops long, Assists can be extremely deleterious to performance and they can be avoided in many cases.

Possible Issues

A significant portion of execution time is spent in microcode assists.
Tips:
1. Examine the FP_ASSIST and OTHER_ASSISTS events to determine the specific cause.
2. Add options eliminating x87 code and set the compiler options to enable DAZ (denormals-are-zero) and FTZ (flush-to-zero).

Product and Performance Information

1

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