Making read-copy update free-running grace period counters safe against lengthy low power state sojourns

摘要

A technique for making a free-running grace period counter safe against lengthy low power state processor sojourns. The grace period counter tracks grace periods that determine when processors that are capable executing read operations have passed through a quiescent state that guarantees the readers will no longer maintain references to shared data. Periodically, one or more processors may be placed in a low power state in which the processors discontinue performing grace period detection operations. Such processors may remain in the low power state for a complete cycle of the grace period counter. This scenario can potentially disrupt grace period detection operations if the processors awaken to see the same grace period counter value. To rectify this situation, processors in a low power state may be periodically awakened at a predetermined point selected prevent the low power state from extending for an entire roll over of the grace period counter.