User Guide


Machine Clears

Metric Description

Certain events require the entire pipeline to be cleared and restarted from just after the last retired instruction. This metric measures three such events: memory ordering violations, self-modifying code, and certain loads to illegal address ranges. Machine Clears metric represents slots fraction the CPU has wasted due to Machine Clears. These slots are either wasted by uOps fetched prior to the clear, or stalls the out-of-order portion of the machine needs to recover its state after the clear.

Possible Issues

A significant portion of execution time is spent handling machine clears.


Examine the MACHINE_CLEARS events to determine the specific cause. See the "Memory Disambiguation" section in the
Intel 64 and IA-32 Architectures Optimization Reference Manual
for more details.

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