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JILP
2000

Speculative Updates of Local and Global Branch History: A Quantitative Analysis

13 years 3 months ago
Speculative Updates of Local and Global Branch History: A Quantitative Analysis
In today's wide-issue processors, even small branch-misprediction rates introduce substantial performance penalties. Worse yet, inadequate branch prediction creates a bottleneck at the fetch stage, restricting other opportunities for improving performance. The choice of how to predict conditional-branch outcomes is the primary lever on prediction accuracy. But the choice of when to update the predictor with branch outcomes is a second powerful lever, and the subject of this paper. In history-based predictors like gshare, many mispredictions result from commit-time update of the history: typical pipelined processors predict branches in the fetch stage, but update the predictor in the commit stage, making the predictor's state temporarily outof-date. As pipelines grow longer--in particular, when branches can spend many cycles in the instruction window waiting to issue--this problem becomes worse. Prior work on this subject has discussed the need for speculative update in a glo...
Kevin Skadron, Margaret Martonosi, Douglas W. Clar
Added 19 Dec 2010
Updated 19 Dec 2010
Type Journal
Year 2000
Where JILP
Authors Kevin Skadron, Margaret Martonosi, Douglas W. Clark
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