SIMT Load Gather Buffer for Cache Hit-Miss Coalescing
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Solution Overview
Problem
Existing graphics processors face inefficiencies in bus transactions and power consumption due to complex cache hierarchies handling multiple memory spaces, particularly in unified memory architectures, where cache accesses can result in both hits and misses, leading to increased bandwidth and power usage.
Innovation Solution
Implementing deterministic load gathering techniques for cache hits and non-deterministic miss gather control to consolidate data from multiple memory spaces, reducing bus transactions and optimizing power consumption by ensuring all hit data is gathered before transmission, while allowing misses to be gathered based on event triggers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If cache hierarchies handle multiple memory spaces with separate data gathering for each space, then data access accuracy is improved, but bus transaction complexity and power consumption increase
Solution Approach 1:
The patent merges the data gathering process for multiple memory spaces into a single unified load gathering operation. Instead of handling cache hits and misses from different memory spaces separately, the system consolidates all such operations into one gather buffer, reducing bus transaction complexity while maintaining accurate data retrieval from multiple spaces.
Solution Approach 2:
The load gather buffer is designed as a universal structure that handles multiple memory spaces (global memory, L2 cache, register files) through a single interface. This multi-functional approach allows the same gathering mechanism to serve different memory sources, reducing the need for separate specialized paths and thereby reducing overall system complexity.
2Stability of the object's composition
If deterministic load gathering is implemented for all cache accesses, then data handling consistency is improved, but processing time for cache misses increases
Solution Approach 1:
The system dynamically adjusts the gathering strategy based on cache access results. For cache hits, deterministic gathering is applied to ensure consistency. For cache misses, the system uses a timeout mechanism that allows flexible, non-deterministic gathering, enabling faster processing when needed while maintaining consistency when required. This dynamic approach resolves the contradiction between consistency and speed.
Solution Approach 2:
The patent changes the gathering parameter from strict determinism to a flexible model based on cache hit/miss status and timeout conditions. By parameterizing the gathering behavior according to the access outcome, the system can optimize both consistency (for hits) and speed (for misses with timeouts), resolving the time-consistency tradeoff.
3Reliability
If separate data gathering paths are maintained for cache hits and misses, then data retrieval accuracy is improved, but cache buffer size requirements increase
Solution Approach 1:
The patent combines separate data gathering paths into a single unified load gather buffer that handles both cache hits and misses. This merging eliminates the need for duplicate buffer structures, reducing the total cache buffer size requirement while maintaining accurate data retrieval through a single consolidated gathering mechanism.
4Reliability
If multiple granular writes are performed to next cache level, then data completeness is improved, but bandwidth consumption increases
Solution Approach 1:
The load gather buffer performs preliminary gathering and consolidation of data from multiple memory spaces before transmitting to the next cache level. By pre-aggregating the data in a unified structure, the system reduces the number of separate write operations needed, thereby reducing bandwidth consumption while maintaining data completeness through the comprehensive gather operation.
Data Source
AI summary
In some embodiments, an apparatus includes execution circuitry configured to execute threads of single-instruction multiple-thread (SIMT) groups. Cache circuitry stores data for multiple registers of a given thread. Coalesce circuitry determines cache line information for SIMT load instructions, while tag circuitry identifies cache hits and misses. Load gather buffer circuitry buffers register data for hits, tracks expected and completed cache line requests, and transmits retrieved data upon completion. The apparatus processes requests with multiple memory addresses, data sizes, and cache line byte offsets. Additional features include rotated gather buffer alignment for parallel read/write support, transpose circuitry for aligning data, and miss gather circuitry with scoreboard tracking and timeout controls for handling cache misses.