Hardware Reservation Register for Command Queue Synchronization
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Solution Overview
Problem
Existing systems face challenges in efficiently distributing and synchronizing processing loads across multiple processing elements due to high processing overhead from software-based synchronization techniques, such as semaphores and mutexes, which can lead to overfilled command queues and increased time from command issuance to execution.
Innovation Solution
A hardware-based system utilizing a reservation register to manage available space in command queues, allowing processing elements to reserve space before issuing commands, thereby reducing software overhead and ensuring synchronization without queue overflow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If software techniques (semaphores and mutexes) are used for synchronization among multiple processing elements, then queue overflow can be prevented, but processing time increases and synchronization overhead increases
Solution Approach 1:
The patent replaces software-based synchronization mechanisms (semaphores and mutexes) with a hardware-based arbitration circuit. The arbitration circuit directly monitors command queue status and automatically grants command issuance rights to processing elements, eliminating the need for software synchronization overhead while maintaining queue overflow prevention.
Solution Approach 2:
The patent introduces an intermediary arbitration circuit that sits between multiple processing elements and the command queue. This arbitration mechanism mediates access requests from multiple processing elements, granting permission to issue commands only when the queue has available space, thus preventing overflow without requiring software intervention.
2Productivity
If processing load determination is distributed to multiple processing elements, then processing throughput increases, but synchronization complexity increases and queue management becomes more difficult
Solution Approach 1:
The patent merges the synchronization functions of multiple processing elements into a single centralized arbitration circuit. While multiple processing elements can independently determine commands and attempt to issue them, the arbitration circuit consolidates the coordination of these elements, managing queue access rights centrally and simplifying the overall synchronization complexity.
3Speed
If command queue depth is kept shallow to minimize command issue to execution time, then latency is reduced, but queue capacity is limited and processing throughput may be constrained
Solution Approach 1:
The patent implements dynamic queue depth management where the command queue depth can be adjusted based on system conditions. The arbitration circuit monitors queue status and dynamically controls command issuance permissions, allowing the system to optimize between shallow queue operation (for low latency) and deeper queue utilization (for high throughput) depending on current processing demands and queue occupancy.
Data Source
AI summary
A shared counter resource, such as a register, is disclosed in the hardware, where the register representing how much free space there is in the command queue is accessible to one or more processing elements. When a processing element reads the “reservation” register, the hardware automatically decrements the available free space by a preconfigured amount (e.g., 1) and returns the value of the free space immediately prior to the read/reservation. If the read returns 0 (or a number less than the preconfigured amount), there was insufficient free space to satisfy the request. In the event there was insufficient space to satisfy the request the reservation register may be configured to reserve however much space was available or to not reserve any space at all. Any number of processing elements may read these registers and various scenarios are described where the input and output queues are accessible via various processing elements.