An analysis of the performance impact of wrong-path memory references on out-of-order and runahead execution processors

High-performance, out-of-order execution processors spend a significant portion of their execution time on the incorrect program path even though they employ aggressive branch prediction algorithms. Although memory references generated on the wrong path do not change the architectural state of the p...

Full description

Saved in:
Bibliographic Details
Published in:IEEE transactions on computers 2005-12, Vol.54 (12), p.1556-1571
Main Authors: Mutlu, O., Kim, H., Armstrong, D.N., Patt, Y.N.
Format: Article
Language:English
Subjects:
Benchmarks
Cache memories
Computer instructions
Errors
Estimates
Hierarchies
Index Terms- Single data stream architectures
Interprocessor communication
Mathematical models
Parallel architectures
Pollution abatement
processor performance modeling
Processors
runahead execution
speculative execution
Studies
Citations: Items that this one cites
Items that cite this one
Online Access:Get full text
Tags: Add Tag
No Tags, Be the first to tag this record!
Description
Summary:High-performance, out-of-order execution processors spend a significant portion of their execution time on the incorrect program path even though they employ aggressive branch prediction algorithms. Although memory references generated on the wrong path do not change the architectural state of the processor, they affect the arrangement of data in the memory hierarchy. This paper examines the effects of wrong-path memory references on processor performance. It is shown that these references significantly affect the IPC (instructions per cycle) performance of a processor. Not modeling them leads to errors of up to 10 percent (4 percent on average) in IPC estimates for the SPEC CPU2000 integer benchmarks on an out-of-order processor and errors of up to 63 percent on a runahead-execution processor. In general, the error in the IPC increases with increasing memory latency and instruction window size. We find that wrong-path references are usually beneficial for performance because they prefetch data that is used by later correct-path references. L2 cache pollution is found to be the most significant negative effect of wrong-path references. Code examples are shown to provide insights into how wrong-path references affect performance. We also show that it is crucial to model wrong-path references to accurately estimate the performance improvement provided by runahead execution.
ISSN:0018-9340
1557-9956
DOI:10.1109/TC.2005.190