International Business Machines Corporation

Kevin A Closson

Paul Edward McKenney

Raghupathi Malige

The processors in a multiprocessor computer system are grouped into nodes. The processors can request a lock, but the lock is granted to only one processor at any given time to provide exclusive processor access to the resource protected by the lock. When a processor releases the lock, the lock is made available to another processor at the same node, even though a processor at a different node may have requested the lock earlier. To maintain fairness, the lock is forced to another node after granting a certain number of consecutive requests at a node or after a certain time period. In one embodiment, a specialized data structure representing a lock request from a processor at a particular node is placed into a queue. A later requesting processor can acquire a preemptive position in the queue by spinning on a data structure already in the queue if the data structure corresponds to the processor's node. To maintain fairness, the data structure is limited to a certain number of uses, after which additional processors are not permitted to spin on it. When the data structure has no more active spinners, it is dequeued, and the lock is made available to a processor spinning on the next structure in the queue. Logic for handling interrupts is included, and the bitfield arrangement of the data structure is tailored to the locking scheme. Preallocating data structures for the queue increases performance.

Lingering locks with fairness control for multi-node computer systems

A buffer cache management structure, or metadata, for a computer system such as a NUMA (non-uniform memory access) machine, wherein physical main memory is distributed and shared among separate memories. The memories reside on separate nodes that are connected by a system interconnect. The buffer cache metadata is partitioned into portions that each include a set of one or more management data structures such as hash queues that keep track of disk blocks cached in the buffer cache. Each set of management data structures is stored entirely within one memory. A first process performs operations on the buffer cache metadata by determining, from an attribute of a data block requested by the process, in which memory a portion of the metadata associated with the data block is stored. The process then determines if the memory containing the metadata portion is local to the process. If so, the first process performs the operation. If not, the first process requests that a second process that is local to the memory perform the operation. The second process then performs the operation and notifies the first process of the operation results.

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Forest Grove, OR, United States of America

Kevin A Closson