Computer mechanism for reducing dasd arm contention during parallel

Abstract

In parallel process computer systems multiple tasks are simultaneously executed. However, where resource contention exists, the multiple tasks become serialized, reducing system performance. Once such resource contention is arm contention during reads for files stored under multiple arms on direct access storage devices (DASDs). According to the preferred embodiment, a method is provided that assigns read tasks in a manner that reduces the probability of arm contention during the file reads. First, the plurality of extents storing the file are correlated to their associated arm. Second, for each of the plurality of arms, the attributes of extents under that arm, preferably including the extent read times, are accumulated. Finally, the plurality of simultaneous read tasks are assigned to the plurality of extents according to the accumulated attributes such that arms that have a greater need for service are favored over arms that have a lesser need when reading the file. Assigning the tasks in this manner lessons the probability of arm contention during file reads, increasing system performance.