Title
Bypass and insertion algorithms for exclusive last-level caches
Abstract
Inclusive last-level caches (LLCs) waste precious silicon estate due to cross-level replication of cache blocks. As the industry moves toward cache hierarchies with larger inner levels, this wasted cache space leads to bigger performance losses compared to exclusive LLCs. However, exclusive LLCs make the design of replacement policies more challenging. While in an inclusive LLC a block can gather a filtered access history, this is not possible in an exclusive design because the block is de-allocated from the LLC on a hit. As a result, the popular least-recently-used replacement policy and its approximations are rendered ineffective and proper choice of insertion ages of cache blocks becomes even more important in exclusive designs. On the other hand, it is not necessary to fill every block into an exclusive LLC. This is known as selective cache bypassing and is not possible to implement in an inclusive LLC because that would violate inclusion. This paper explores insertion and bypass algorithms for exclusive LLCs. Our detailed execution-driven simulation results show that a combination of our best insertion and bypass policies delivers an improvement of up to 61.2% and on average (geometric mean) 3.4% in terms of instructions retired per cycle (IPC) for 97 single-threaded dynamic instruction traces spanning selected SPEC 2006 and server applications, running on a 2 MB 16-way exclusive LLC compared to a baseline exclusive design in the presence of well-tuned multi-stream hardware prefetchers. The corresponding improvements in throughput for 35 4-way multi-programmed workloads running with an 8 MB 16-way shared exclusive LLC are 20.6% (maximum) and 2.5% (geometric mean).
Year
DOI
Venue
2011
10.1145/2000064.2000075
Computer Architecture
Keywords
Field
DocType
cache space,exclusive last-level cache,exclusive design,baseline exclusive design,inclusive llc,geometric mean,cache block,mb 16-way,insertion algorithm,cache hierarchy,exclusive llcs,exclusive llc,servers,resource management,integrated circuit design,least recently used,algorithm design and analysis,ipc,hardware,coherence
Cache hierarchy,Algorithm design,Cache,Computer science,Parallel computing,Server,Algorithm,Real-time computing,Integrated circuit design,Throughput,Spec#,Operating system
Conference
Volume
Issue
ISSN
39
3
0163-5964
ISBN
Citations 
PageRank 
978-1-4503-0472-6
55
1.31
References 
Authors
19
3
Name
Order
Citations
PageRank
Jayesh Gaur11086.98
Mainak Chaudhuri230018.86
Sreenivas Subramoney312713.60