Computers as Components by Marilyn Wolf

Author:Marilyn Wolf
Language: eng
Format: epub
ISBN: 9780123884428
Publisher: Elsevier Science
Published: 2012-05-25T16:00:00+00:00

Figure 5.19 A reservation table for instruction scheduling.

We can also schedule instructions to maximize performance. As we know from Section 3.6, when an instruction that takes more cycles than normal to finish is in the pipeline, pipeline bubbles appear that reduce performance. Software pipelining is a technique for reordering instructions across several loop iterations to reduce pipeline bubbles. Some instructions take several cycles to complete; if the value produced by one of these instructions is needed by other instructions in the loop iteration, then they must wait for that value to be produced. Rather than pad the loop with no-ops, we can start instructions from the next iteration. The loop body then contains instructions that manipulate values from several different loop iterations—some of the instructions are working on the early part of iteration n + 1, others are working on iteration n, and still others are finishing iteration n − 1.

Instruction selection

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