Predicated Compute Thread Launch via Pushbuffer Control
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Solution Overview
Problem
Existing systems lack a mechanism to efficiently predicate the launch of compute thread arrays in processing architectures, leading to unnecessary processing and potential race conditions due to the lack of control over the execution of subsequent threads based on the results of preceding threads.
Innovation Solution
The implementation of a pushbuffer mechanism that allows for the queuing and controlled launching of predicated processes, using a semaphore data structure to determine whether to execute subsequent threads based on a predicate generated by a preceding thread, enabling or disabling launch commands globally or specifically.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If launch commands for multiple threads are loaded into the pushbuffer, then the system can prepare and queue multiple compute operations, but unnecessary threads may be launched consuming processing resources without being needed
Solution Approach 1:
The system performs preliminary actions by loading all launch commands into the pushbuffer in advance, including commands for threads that may not be needed. The predicate mechanism then selectively enables or disables these pre-loaded commands based on runtime conditions, allowing the system to prepare work ahead while avoiding unnecessary execution.
Solution Approach 2:
The predicate value stored in memory provides dynamic control over thread launch decisions. Instead of static launch behavior, the system dynamically determines whether to execute subsequent launch commands based on the predicate value, allowing adaptive resource allocation based on actual runtime needs.
2Speed
If subsequent threads are launched without checking previous thread results, then processing can proceed in parallel, but race conditions may occur due to lack of execution control
Solution Approach 1:
The predicate value stored in memory acts as an intermediary between the first thread's execution results and the subsequent thread's launch decision. This intermediary mechanism allows parallel processing to proceed while maintaining execution control, as the predicate value determines whether subsequent threads should launch based on the first thread's outcome.
Solution Approach 2:
The system implements feedback control by having the first thread's execution results (stored as a predicate value in memory) influence the launch decisions of subsequent threads. This feedback mechanism ensures that parallel processing maintains proper execution control and avoids race conditions by conditioning thread launches on actual runtime results.
3Loss of energy
If a predicate mechanism is implemented to selectively enable/disable thread launches, then unnecessary processing is prevented, but additional memory access and control logic are required
Solution Approach 1:
The control logic for predicate-based thread selection is extracted from the thread launch execution path and implemented as a separate memory read operation. The predicate value is stored in memory and read independently to determine launch decisions, separating the control logic from the execution path and reducing the complexity burden on the processing units.
Solution Approach 2:
Memory serves as an intermediary storage mechanism for the predicate value, decoupling the predicate generation (from the first thread's results) from the predicate consumption (in the subsequent thread launch decisions). This intermediary approach simplifies the control logic by using memory as a buffer rather than requiring complex inter-thread communication protocols.
Data Source
AI summary
A controlling process may enable or disable the launching of a predicated process that has already been queued for launching, e.g. via a pushbuffer. The controlling process generates a report so that launching of the predicated process is enabled or disabled based on the report. The predicate may be global in application to enable or disable all subsequent launch commands. Alternatively, the predicate may be specific to one or more predicated processes. In an embodiment with a central processing unit (CPU) coupled to a graphics processing unit (GPU), the CPU may generate the controlling process that enables or disables the launch of the predicated process. Alternatively or additionally, the GPU may generate the controlling process that enables or disables the launch of the predicated process.