User-Level Thread Suspend Instruction for Low-Latency Memory Monitoring
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Solution Overview
Problem
Existing methods for software threads to monitor changes in shared memory locations, such as polling loops or sleeping, are inefficient for medium-duration wait times, consuming power and resources without optimal responsiveness and latency.
Innovation Solution
The introduction of user-level suspend thread instructions, including the user-level monitored access suspend thread instruction, allows threads to suspend execution without polling or transitioning to supervisory software, using a monitor mechanism to detect changes in shared memory locations with reduced latency and power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If polling loops are used to monitor shared memory locations, then threads can detect changes, but power consumption increases and responsiveness deteriorates for medium-duration wait times
Solution Approach 1:
The patent implements periodic monitoring of shared memory locations through hardware-based monitor instructions that check for changes at optimized intervals. Instead of continuous polling, the system uses periodic interrupts or trap mechanisms that wake the thread only when memory changes occur, reducing power consumption while maintaining reliable detection of shared memory modifications.
Solution Approach 2:
The patent introduces hardware monitor instructions and monitor structures as intermediaries between threads and shared memory locations. These monitor mechanisms act as mediators that detect memory changes and notify threads without requiring threads to continuously poll, thereby reducing power consumption while maintaining reliable change detection.
2Reliability
If polling loops are used to monitor shared memory locations, then threads can detect changes, but responsiveness and latency worsen for medium-duration wait times
Solution Approach 1:
The system uses periodic monitoring with interrupt-based notifications that allow threads to sleep between checks. When memory changes occur, the hardware generates an interrupt that wakes the thread immediately, reducing latency compared to continuous polling while maintaining reliable detection through the periodic check mechanism.
Solution Approach 2:
Hardware monitor instructions serve as intermediaries that detect memory changes and trigger interrupts or traps to notify threads. This intermediary mechanism reduces latency by immediately notifying threads of changes rather than waiting for the next polling cycle, while maintaining reliable detection through the hardware-based monitoring.
3Reliability
If threads transition to supervisory software for monitoring, then monitoring can be performed, but processor utilization decreases and resource occupation increases
Solution Approach 1:
The patent enables user-level threads to perform self-service monitoring through hardware-based monitor instructions that operate at user mode without requiring transitions to supervisory software. The monitor instructions directly detect shared memory changes and notify threads through interrupts or traps, allowing threads to maintain monitoring capability while remaining in user mode and thus improving processor utilization.
Solution Approach 2:
Hardware monitor instructions and monitor structures act as intermediaries that provide monitoring capability at user level without requiring supervisory software intervention. These intermediaries enable threads to monitor shared memory locations independently, maintaining reliable monitoring while avoiding the overhead of mode transitions and improving overall processor utilization.
Data Source
AI summary
A processor of an aspect includes a decode unit to decode a user-level suspend thread instruction that is to indicate a first alternate state. The processor also includes an execution unit coupled with the decode unit. The execution unit is to perform the instruction at a user privilege level. The execution unit in response to the instruction, is to: (a) suspend execution of a user-level thread, from which the instruction is to have been received; (b) transition a logical processor, on which the user-level thread was to have been running, to the indicated first alternate state; and (c) resume the execution of the user-level thread, when the logical processor is in the indicated first alternate state, with a latency that is to be less than half a latency that execution of a thread can be resumed when the logical processor is in a halt processor power state.