CXL Memory Controller Dynamic Flit Packing
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Solution Overview
Problem
The efficiency of data transmission in a memory system configured as a Compute Express Link (CXL) device is limited by the packing of response commands with and without data into Flits, which affects the overall transmission efficiency to the host.
Innovation Solution
The memory system employs a controller that packs response commands with data (DRS) and without data (NDR) into Flits, using a slot format selector and transmit Flit generator to optimize the packing based on the remaining number of data slots, DRS, and NDR, thereby selecting the most efficient format for each Flit to be transmitted to the CXL ARB/MUX layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If response commands are packed into Flits using traditional first-in, first-out packing methods, then the transmission process is simple, but the transmission efficiency is low and the number of Flits required is high
Solution Approach 1:
The patent implements dynamic Flit packing by selecting different slot formats (H0-H7, G0-G7) based on real-time conditions including remaining data slots, DRS count, NDR count, and empty slots. This dynamic adaptation allows the system to optimize packing efficiency for each Flit while maintaining manageable control complexity through structured decision logic.
Solution Approach 2:
The patent changes multiple parameters simultaneously to optimize packing: slot format selection, Flit type determination (protocol vs. all-data), and transmission ordering. By adjusting these parameters based on current buffer states and command characteristics, the system achieves superior transmission efficiency compared to static first-in, first-out methods.
2Loss of time
If the number of Flits is reduced through optimized packing, then transmission time decreases, but the packing decision process becomes more complex
Solution Approach 1:
The patent performs preliminary actions by pre-defining multiple slot formats (H0-H7 for header slots, G0-G7 for generic slots) with specific characteristics for packing DRS and NDR. This preliminary structuring enables efficient real-time selection without requiring complex runtime calculations, thus reducing transmission time while keeping the selection process manageable.
Solution Approach 2:
The patent uses feedback from the current system state (remaining data slots, DRS count, NDR count, empty slots) to dynamically select optimal slot formats and packing strategies. This feedback mechanism allows the system to adapt to varying conditions and minimize Flit count without requiring exhaustive search algorithms, balancing complexity and efficiency.
3Productivity
If multiple slot formats are used for packing DRS and NDR, then packing efficiency improves, but the difficulty of detecting and measuring the optimal format increases
Solution Approach 1:
The patent segments the slot format selection into distinct categories: header slots (H0-H7) for packing DRS and generic slots (G0-G7) for data. This segmentation simplifies the detection and measurement process by providing clear guidelines for when to use each slot type based on the current command buffer state, making the complex multi-format system manageable.
Solution Approach 2:
The patent applies different slot formats locally based on specific conditions: H slots when DRS needs to be packed with headers, G slots for pure data transmission, and specific formats based on the combination of DRS and NDR counts. This local quality approach ensures optimal packing efficiency for each situation without requiring global optimization algorithms.
Data Source
AI summary
According to one embodiment, a memory system is connectable to a host as a type 3 compute express link (CXL) device. A controller of the memory system packs, at a CXL link layer, a response command with data (DRS) and/or a response command without data (NDR), received from an upper CXL transaction layer, into a flit including four slots, and transmits the response command to a lower CXL ARB/MUX layer, and selects, based on a remaining number of data slots of DRS packed in a first flit that has been transmitted to the CXL ARB/MUX layer, a remaining number of DRS, a remaining number of NDR, and a number of empty slots in a second flit to be transmitted subsequently to the CXL ARB/MUX layer, a format to be used in slots in a second flit.