On Reusing the Results of Pre-Executed Instructions in a Runahead Execution Processor

Previous research on runahead execution took it for granted as a prefetch-only technique. Even though the results of instructions independent of an L2 miss are correctly computed during runahead mode, previous approaches discarded those results instead of trying to utilize them in normal mode execution. This paper evaluates the effect of reusing the results of preexecuted instructions on performance. We find that, even with an ideal scheme, it is not worthwhile to reuse the results of preexecuted instructions. Our analysis provides insights into why result reuse does not provide significant performance improvement in runahead processors and concludes that runahead execution should be employed as a prefetching mechanism rather than a full-blown prefetching/result-reuse mechanism.