DTLB Overhead

Metric Description

In x86 architectures, mappings between virtual and physical memory are facilitated by a page table, which 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. This metric estimates the performance penalty paid for missing the first-level data TLB (DTLB) that includes hitting in the second-level data TLB (STLB) as well as performing a hardware page walk on an STLB miss.

Possible Issues

A significant proportion of cycles is being spent handling first-level data TLB misses.

Tips

1. As with ordinary data caching, focus on improving data locality and reducing the working-set size to minimize the DTLB overhead.

2. Consider using profile-guided optimization (PGO) to collocate frequently-used data on the same page.

3. Try using larger page sizes for large amounts of frequently-used data.

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