Adaptive RDMA Acknowledgement Coalescing for Interrupt Overhead

Solution Overview

Problem

Current RDMA implementations send acknowledgments at a constant rate, leading to equal latency for both latency-sensitive and high-throughput applications, resulting in inefficient processor utilization and interrupt overhead, as they do not adapt to varying I/O characteristics of different applications.

Innovation Solution

The adaptive coalescing method determines the acknowledgement frequency for RDMA requests on a per-Queue Pair basis by analyzing I/O characteristics such as I/O type, rate, and size, allowing for adaptive acknowledgement coalescing, reducing interrupt overhead and improving processor utilization by varying the acknowledgement rate based on specific application requirements.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If acknowledgements are sent at a constant rate for all RDMA connections, then implementation simplicity is maintained, but processor utilization efficiency deteriorates due to unnecessary interrupt overhead for high-throughput applications and insufficient responsiveness for latency-sensitive applications

Engineering Contradiction:

Improveprocessor utilization efficiencyVSAvoidacknowledgement frequency control complexity

Core Design Contradiction:

ProductivityVSDevice complexity

Solution Approach 1:

The system dynamically adjusts the acknowledgement frequency based on the I/O characteristics of each Queue Pair. Instead of using a fixed constant rate, the acknowledgement frequency is adapted in real-time according to the specific needs of each application, allowing high-throughput applications to benefit from reduced interrupt overhead while latency-sensitive applications maintain high responsiveness

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The system applies different acknowledgement frequencies to different Queue Pairs based on their individual I/O characteristics. Each Queue Pair receives a customized acknowledgement strategy tailored to its specific application requirements, rather than applying a uniform approach across all connections

Inventive Principle:

Principle #3Local quality

2Speed

If acknowledgements are sent frequently to ensure low latency for latency-sensitive applications, then latency performance is improved, but interrupt overhead increases and processor utilization efficiency deteriorates for high-throughput applications

Engineering Contradiction:

Improvelatency performanceVSAvoidinterrupt overhead

Core Design Contradiction:

SpeedVSLoss of energy

Solution Approach 1:

The system dynamically adjusts the acknowledgement frequency based on the I/O characteristics of each Queue Pair. Instead of using a fixed constant rate, the acknowledgement frequency is adapted in real-time according to the specific needs of each application, allowing high-throughput applications to benefit from reduced interrupt overhead while latency-sensitive applications maintain high responsiveness

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The system changes the acknowledgement frequency parameter based on the I/O characteristics of each Queue Pair. By analyzing factors such as I/O rate and pattern, the system adjusts this critical parameter to optimize the balance between latency performance and interrupt overhead for each specific connection

Inventive Principle:

Principle #35Parameter changes

3Loss of energy

If acknowledgements are sent at a low frequency to reduce interrupt overhead for high-throughput applications, then processor utilization is improved, but latency performance deteriorates for latency-sensitive applications

Engineering Contradiction:

Improveinterrupt overheadVSAvoidlatency performance

Core Design Contradiction:

Loss of energyVSSpeed

Solution Approach 1:

The system applies different acknowledgement frequencies to different Queue Pairs based on their individual I/O characteristics. Each Queue Pair receives a customized acknowledgement strategy tailored to its specific application requirements, rather than applying a uniform approach across all connections

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The system monitors the I/O characteristics of each Queue Pair and uses this feedback to adjust the acknowledgement frequency. By continuously observing the traffic patterns and performance metrics, the system can adaptively tune the acknowledgement rate to maintain optimal latency performance while minimizing interrupt overhead

Inventive Principle:

Principle #23Feedback

Data Source

PatentUS9965441B2Adaptive coalescing of remote direct memory access acknowledgements based on I/O characteristics

Publication Date: 2018.05.08 CISCO TECHNOLOGY INC

AI summary

An example method for adaptively coalescing remote direct memory access (RDMA) acknowledgements is provided. The method includes determining one or more input/output (I/O) characteristics of RDMA packets of a plurality of queue pairs (QPs) on a per-QP basis, each QP identifying a respective RDMA connection between a respective first compute node and a respective second compute node. The method further includes determining an acknowledgement frequency for providing acknowledgements of the RDMA packets on a per-QP basis (i.e., a respective acknowledgement frequency is set for each QP) based on the determined one or more I/O characteristics for each QP.