Zero-Content Augmented Caches

Julien Dusser (1) , Thomas Piquet (1) , André Seznec (1)

1 CAPS - Compilation, parallel architectures and system

It has been observed that some applications manipulate large amounts of null data. Moreover these zero data often exhibit high spatial locality. On some applications more than 20% of the data accesses concern null data blocks. Representing a null block in a cache on a standard cache line is clearly a waste of resources. In this paper, we propose the Zero-Content Augmented cache, the ZCA cache. A ZCA cache consists of a conventional cache augmented with a specialized cache for memorizing null blocks, the Zero-Content cache or ZC cache. In the ZC cache, the data block is represented by its address tag and a validity bit. Moreover, as null blocks generally exhibit high spatial locality, several null blocks can be associated with a single address tag in the ZC cache. For instance, a ZC cache mapping 32MB of zero 64-byte lines uses less than 80KB of storage. Decompression of a null block is very simple, therefore read access time on the ZCA cache is in the same range as on a conventional cache. On applications manipulating large amount of null data blocks, such a ZC cache allows to reduce up to 81% the miss rate and memory traffic, and therefore to increase performance for a small hardware overhead. In particular, the writeback traffic on null blocks is limited. For applications with a low null block rate no performance loss is observed.

Domaines: Architectures Matérielles [cs.AR]

Julien Dusser, Thomas Piquet, André Seznec. Zero-Content Augmented Caches. [Research Report] RR-6705, INRIA. 2008. ⟨inria-00337742⟩