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Method for a backup mechanism through temporary column override of dependency matrices

IP.com Disclosure Number: IPCOM000028870D
Publication Date: 2004-Jun-04
Document File: 3 page(s) / 37K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for a backup mechanism through temporary column override of dependency matrices. Benefits include improved functionality and improved performance

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Method for a backup mechanism through temporary column override of dependency matrices

Disclosed is a method for a backup mechanism through temporary column override of dependency matrices. Benefits include improved functionality and improved performance.

Background

              Basic out-of-order schedulers can be divided into two groups:

•             Dynamic schedulers that watch for the completion of instructions to schedule dependent instructions

•             Static schedulers that resolve instruction dependencies before any instruction is scheduled

      Conventionally, static schedulers resolve dependencies by checking the source and destination register IDs of all instructions in a particular scheduling window. However, a problem occurs if the parent instruction is a load instruction that has a variable execution latency, depending on where it hits in the cache hierarchy. Static schedulers solve this problem by waiting for a load instruction to complete before scheduling dependent operations. Alternatively, the scheduler assumes that the load instruction hits the cache and replays all dependent instructions if the load instruction is actually missed. Instructions are deallocated from the scheduler and, if the load instruction missed the predicted cache, they are reinserted into the scheduler at a later time. This procedure requires the presence of a temporary holding buffer and complex arbitration logic to choose between the rescheduled operations and the operations entering the scheduler.

Description

              The disclosed method enables a scheduler’s dependency matrix to be restored quickly. As a result, instructions in the shadow of a mispredicted load can be replayed from the scheduler and do not require a holding buffer.

              The disclosed method uses column override logic to temporarily clear a column in a dependency matrix. In each column, one flop stores the status of a column overrid...