GPU Texture Sampler Out-of-Order Scheduling for Cache Latency
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Solution Overview
Problem
Texture sampler operations in GPUs are latency-sensitive due to variable operation lengths, leading to inefficiencies in in-order pipelines, which are limited by cache size or thread count, and scaling solutions are costly and prohibitive.
Innovation Solution
Implementing an out-of-order execution mechanism for GPU texture sampler operations using virtual channels (VCs) that arbitrate transactions once data is available in the L1 cache, with a latency queue and multiple VC queues to facilitate out-of-order processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If an in-order pipeline is used for texture sampler operations, then the pipeline is simple to implement, but performance deteriorates due to latency sensitivity and variable operation lengths
Solution Approach 1:
The patent segments the texture sampler pipeline into multiple virtual channels (VC0, VC1, VC2, etc.), each handling specific operations independently. This allows out-of-order execution where different virtual channels can process transactions at different rates, resolving the contradiction between pipeline simplicity and performance by introducing controlled complexity only where needed.
Solution Approach 2:
The patent introduces dynamic arbitration mechanisms that allow the pipeline to adapt its behavior based on transaction status. The virtual channel arbitration unit dynamically selects which channel to process next based on availability and priority, enabling the system to respond to variable operation lengths without compromising overall throughput.
2Productivity
If the pipeline is made more complex to handle variable operation lengths, then productivity improves, but device complexity increases
Solution Approach 1:
The virtual channel arbitration unit serves multiple functions: it arbitrates between different virtual channels, manages transaction priorities, and coordinates cache access. This multi-functionality allows the patent to improve productivity through out-of-order execution without proportionally increasing device complexity, as a single arbitration unit handles multiple control tasks.
Solution Approach 2:
The virtual channel arbitration unit acts as an intermediary between the instruction fetch unit and the execution units. It mediates the complexity of out-of-order execution by providing a centralized control mechanism that simplifies the interaction between multiple virtual channels, thus improving productivity while keeping the added complexity manageable.
3Productivity
If cache size is increased to reduce latency, then texture sampler performance improves, but the solution is limited by cost and scalability
Solution Approach 1:
Instead of increasing cache size in the traditional memory hierarchy dimension, the patent introduces a new dimension of virtual channels that operate in parallel. This allows the system to improve memory access performance by processing multiple transactions simultaneously across different virtual channels, achieving scalability without proportionally increasing cache capacity.
Solution Approach 2:
The virtual channels enable preliminary action by allowing transactions to be prepared and queued in advance while waiting for cache availability. The arbitration unit can select which transaction to execute next based on pre-prepared state, reducing actual latency without requiring larger cache structures.
4Reliability
If out-of-order execution is implemented using virtual channels, then latency sensitivity is reduced, but the mechanism becomes more complex
Solution Approach 1:
The execution mechanism is segmented into multiple independent virtual channels, each with its own transaction queue and execution path. This segmentation isolates latency variations in different channels, improving latency consistency for individual transactions while the overall system maintains complexity through the arbitration coordination between channels.
Data Source
AI summary
Embodiments described herein are generally directed facilitating out-of-order execution of GPU texture sampler operations. An embodiment of a method includes a texture sampler of a GPU maintaining (i) a latency queue operable to store information regarding a set of transactions associated with each of multiple texture sampler operations and (ii) multiple virtual channel (VC) queues each operable to store information regarding transactions for a respective single texture sampler operation at a time. Out-of-order processing of the texture sampler operations is facilitated by making use of the latency queue and the VC queues. For example, during a transaction processing interval, the availability of data in a cache for the transactions associated with each of the VC queues may be determined. A VC queue may be selected based on the determined availability of data. A transaction associated with a head of the selected VC queue may then be processed.