Page Walk

Metric Description

In x86 architectures, mappings between virtual and physical memory are facilitated by a page table that is kept in memory. To minimize references to this table, recently-used portions of the page table are cached in a hierarchy of 'translation look-aside buffers', or TLBs, which are consulted on every virtual address translation. As with data caches, the farther a request has to go to be satisfied, the worse the performance impact is. This metric estimates the performance penalty paid for missing the first-level TLB that includes hitting in the second-level data TLB (STLB) as well as performing a hardware page walk on an STLB miss.

Possible Issues

Page Walks have a large performance penalty because they involve accessing the contents of multiple memory locations to calculate the physical address. Since this metric includes the cycles handling both instruction and data TLB misses, look at ITLB Overhead and DTLB Overhead and follow the instructions to improve performance. Also examine PAGE_WALKS.D_SIDE_CYCLES and PAGE_WALKS.I_SIDE_CYCLES events in the source/assembly view for further breakdown. Account for skid.

For more complete information about compiler optimizations, see our Optimization Notice.
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