Don't Use the Page Number, but a Pointer on It
Résumé
Most newly announced microprocessors manipulate 64-bit virtual addresses and the width of physical addresses is also growing. As a result, the relative size of the address tags in the L1 cache is increasing. This is particularly dramatic when small block sizes are used. At the same time, the performance of complex superscalar processors depends more and more on the accuracy of branch prediction, while the size of the Branch Target Buffer is also increasing linearly with the address width. In this paper, we apply the very simple principle enounced in the title for limiting the tag size of on-chip caches, and for limiting the size of the Branch Target Buffer. In an indirect-tagged cache, the anachronic duplication of the page number in processors (in TLB and in cache tags) is removed. The tag check is then simplified and the tag cost does not depend on the address width. Then applying the same principle, we propose the Reduced Branch Target Buffer. The storage size in a Reduced Branch Target Buffer does not depend on the address width and is dramatically smaller than the size of the conventional implementation of a Branch Target Buffer.