Monitoring of shared-resource locks in a multi-processor system with locked-resource bits packed into registers to detect starved threads

Abstract

A resource-lock monitor detects when processors in a multi-processor system are stuck waiting for access to a shared resource. A lock-monitor register has a lock bit and a sticky-lock bit for each processor being monitored. The lock and the sticky-lock bits are both set when the processor executes a lock instruction that also sends a lock-request to a resource arbiter. The lock bit is cleared when the resource arbiter grants access to the processor, but the sticky-lock bit remains set until sticky-lock bits are cleared by monitoring software at the end of a monitoring period. At the end of each monitoring period, monitoring software reads the lock and sticky-lock bits and finds a locked processor when a processor's lock bit is still set, but its sticky-lock bit is cleared. When the locked processor remains locked at the end of another monitoring period, an error handler resets the locked processor.