CSC 456 Fall 2013/1d vb
Trends in Pipelining
Trends of Increasing Pipeline Length
Trends of Decreasing Pipeline Length
The issue with increased pipeline length is the problem of incorrect branch predictions. The longer a pipeline is, the more stages of wasted processing have been wasted when a different branch is taken. Decreasing the pipeline length has resulted in lower clock frequencies, but equal or better IPC. A smaller pipeline suffers less of a loss for every bad prediction, and the overall performance is improved.
An Example of Pipeline changes in Cray Systems
| Year | Name | Pipeline Length | Number of Pipelines |
|---|---|---|---|
| 1976 | Cray 1 | 3 | 12 |
| 2012 | Cray XK7 | 12 for scalar , 17 for vector | 500 cabinets * 24 blades * 4 cores * 3 pipelines per chip |