Adaptive Cut-Through Algorithm for Infiniband Switches
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Solution Overview
Problem
Infiniband switches experience latency due to mismatched link bandwidths between ports, leading to inefficient packet transmission and potential corruption from buffer under-run in conventional store and forward systems.
Innovation Solution
An adaptive cut-through algorithm that calculates a buffer ratio based on input and output port bandwidth characteristics, allowing onward transmission to commence once a sufficient portion of the packet is stored in the output buffer, optimizing latency and preventing buffer under-run.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a store and forward system is used to handle bandwidth mismatch between ports, then data integrity is maintained, but latency increases entirely dependent on packet size
Solution Approach 1:
The patent segments the packet transmission process into two phases: a buffering phase where the initial portion of the packet is stored to ensure data integrity, and a cut-through phase where the remaining portion is transmitted immediately to reduce latency. This segmentation allows the system to simultaneously maintain reliability and minimize time loss by transitioning from complete store-and-forward to partial cut-through based on the calculated buffer ratio.
Solution Approach 2:
The patent dynamically changes the buffering parameter (buffer ratio) based on the bandwidth characteristics of input and output ports. By calculating the buffer ratio as a function of bandwidth mismatch, the system adapts the amount of data to be buffered before cut-through transmission, optimizing the balance between data integrity and latency reduction for different port configurations.
2Loss of time
If cut-through transmission is used to reduce latency, then transmission speed improves, but buffer under-run corruption may occur with bandwidth mismatch
Solution Approach 1:
The patent performs preliminary action by calculating the buffer ratio based on bandwidth characteristics before transmission begins. This pre-calculation determines the exact portion of the packet that must be buffered in advance to prevent buffer under-run corruption during cut-through transmission, ensuring data integrity is maintained while enabling speed improvement.
Solution Approach 2:
The patent applies beforehand cushioning by maintaining a buffer of the calculated ratio portion of the packet before initiating cut-through transmission. This buffer acts as a cushion that prevents buffer under-run corruption when bandwidth mismatch occurs between input and output ports, allowing safe cut-through transmission to proceed with improved latency.
3Reliability
If complete packet storage is used before forwarding, then buffer under-run is prevented, but transmission efficiency decreases due to full packet buffering requirement
Solution Approach 1:
The patent applies partial action by buffering only the necessary portion of the packet (determined by the buffer ratio) rather than the complete packet. This partial buffering is sufficient to prevent buffer under-run corruption while avoiding the excessive buffering of the entire packet, thereby improving transmission efficiency without sacrificing reliability.
Data Source
AI summary
An Infiniband switch can have an input port and a plurality of output ports. The switch can be configured to interrogate at least a header portion of a received packet to determine an output port for the packet and to forward the packet to an output buffer associated with the determined output port. The switch can also be configured to determine an output buffer ratio in dependence upon at least an inbound data rate characteristic of the input port and an outbound data rate characteristic of the determined output port. The output port can be configured to commence onward transmission of the packet once a proportion of the packet conforming to the output buffer ratio has been written into the output buffer.